Everyone can agree that 1+1=2. But the idea that 7 is greater than 13 -- that some numbers are luckier than others -- makes no sense to some people. Such numerical biases can cause deep divisions.

    And that is what happened earlier this month in Hong Kong. Property developer Henderson Land Development Co. made news for selling a condominium for $56.6 million, a price the developer called a residential record in Asia. But after that sale was announced, the property began making news for other unusual numbers. Henderson is labeling the floors of its property at 39 Conduit Road with numbers that increase, but not in the conventional 1-then-2 way. The floor above 39, for example, is 60. And the top three floors are consecutively labeled 66, 68 and 88.

    This offended some people's sense of order. At a protest Sunday against high housing prices, Hong Kong Democratic Party legislators expressed dissatisfaction with the numbering scheme's tenuous relationship to reality. 'You could call the ground floor the 88th floor, but it's meaningless,' says Emily Lau. 'When you say you live on the 88th floor, people expect you to be on the 88th floor, not the 10th floor or something.'

    Numerology, a belief that certain digits have greater meaning beyond merely their quantity, has long been been viewed as a kind of loony uncle to mathematics. Numerologists favor or fear certain numbers depending on factors such as the sound of the words for those numbers or the letter in the alphabet they correspond to. That kind of reasoning leads some mathematicians, who are governed by numerical laws and properties, to believe they have one up on numerologists.

    But many mathematicians have their own emotional attachments to numbers that drove them to enter the field in the first place. Some will cop to having numerical crushes that might not look that different from numerologists'.

    'The idea that numbers are somehow pure and immune to superstitious thinking, because they're somehow more 'objective' than words, doesn't take into account the fact that every concept exists （in our minds） in an interconnected tapestry of emotionally and culturally charged signifiers,' Golan Levin, designer of the interactive project The Secret Lives of Numbers, which tracks the popularity of every whole number between one and one million, writes in an email. He considers most numerical superstitions harmless.

    Thomas Garrity, a mathematician at Williams College, has always had a particular fondness for the number 9. The number 51, however, doesn't make his favorites list.

    'This might stem from childhood, when I regularly thought that 51 should be prime, even though 51=3x17,' he says, taking a trip down mathematical memory lane. But he doesn't base decisions on his preferences, for instance by avoiding the 51st floor of buildings, he says. 'I can understand people having slightly irrational feelings about particular numbers,' Prof. Garrity says. 'I don't get, though, people making real decisions based on such feelings.'

    And yet some numerical superstitions do spread, especially when profits are involved. A Las Vegas casino that caters to Hong Kong high rollers also skips floors from 40 to 59, while Henderson's Hong Kong development omits the 13th floor to cater to Western tastes.

    A Henderson spokeswoman says customers 'don't want the fours and the unlucky numbers. These numbers are more interesting.'

    Henderson chose to name the floors as it did because of positive associations with 6 and 8, and negative ones with 4. In Cantonese and Mandarin, the word for eight sounds like 'faat,' which means prosperity. Hence the Beijing Olympics starting time of 8 p.m. on Aug. 8, 2008. The word for four, meanwhile, 'sounds very much like 'death,' and is therefore avoided at all costs,' says Hung-Hsi Wu, professor emeritus of mathematics at University of California, Berkeley, who was born in Hong Kong. Six is also considered lucky.

    A preference for six over four also guided developers of the 42-floor Mandalay Bay casino in Las Vegas. There, penthouses are on the 60th, 61st and 62nd floor because Mandalay Bay skips the numbers 40 to 59.

    Gordon Absher, spokesman for Mandalay owner MGM Mirage, says that decision was shaped by possible perceptions of high rollers when they are assigned to those floors. 'You could think that we are trying to, as the casino, give you bad luck,' Mr. Absher says.

    Similarly, developers who would assuage fears of 13 can't avoid the existence of a 13th floor in buildings with 13 or more stories. But they can rename it out of existence. When a 13th floor was added to the Skirvin Hotel in Oklahoma City, in the 1930s, it was named the 14th floor. The hotel was shuttered in 1988 and reopened and renamed in 2007 by Hilton, which nonetheless kept the name for the top floor.

    The 22-story headquarters of Chicago-based Marc Realty avoids throwing off the numbers in higher floors by labeling the 13th floor '14A.' It labels the 14th floor '14B.'

    'That arrangement keeps the elevations of the upper floors straight in a physical sense,' says Marc marketing coordinator Dan Krc. He adds that triskaidekaphobia, or fear of 13, appears to be fading, with floors labeled 13 in Marc properties showing occupancy rates are no lower than other floors.

    The negative associations with 13 have been traced to the number of diners at the Last Supper, before the betrayal of Jesus. Some believed it went back to prehistoric times -- the lowest number that couldn't be counted on ten fingers and two feet. （Apparently, individual toes couldn't be counted）.

    But Underwood Dudley, retired professor of mathematics at Depauw University and author of 'Numerology,' says he wasn't able to verify any of these. 'As far as I can tell, some number had to be unlucky, and it was 13,' Dr. Dudley says.

    Beverly Kay, a numerologist in Mequon, Wisc., doesn't buy fears of 13. However, she says her work reading meaning into clients' birth dates and names is consistent with math. 'This is scientific,' Ms. Kay says.

    Psychologists and historians generally have tied such beliefs to the broader human tendency to seek patterns and systems where none exist. At its extreme, an emotional relationship to a number can creep into obsessive-compulsive behavior. In his book 'Strange Brains and Genius,' Clifford Pickover dug through case studies of numerical obsessive-compulsive disorder, and found that it could be tied to just about any numeral. Electricity pioneer Nikola Tesla demanded precisely 18 clean towels a day and showed an intense preference for multiples of three.

    While mathematicians generally don't go to Tesla-like extremes, they possess a generally positive outlook about all numbers and that distinguishes them from numerologists, they say.

    For example, Kenneth Ribet, a professor of mathematics at Berkeley, considers some prime numbers 'friends,' he says. One is 144,169, which reads like 12 squared followed by 13 squared; another the easily remembered number of 1,234,567,891.

    'Mathematicians don't have numbers that they're afraid of or shy away from because we do really like all of the numbers,' says Prof. Ribet. 'On the other hand, some of us have favorites.'

    人人都可以相信，1加1等于2.但7比13好──有些數字比其他數字吉利──對一些人來說就沒有道理了。這種數字上的好惡，可能會造成深刻的分歧。

    上月早些時候，香港就曾發生過這樣一種情況。房地產開發商恒基兆業地產有限公司（Henderson Land Development Co.,簡稱恒基地產）一套復式公寓賣出5660萬美元的天價，轟動一時。恒基地產說，這個數字創了亞洲住宅價格的紀錄。這一銷售結果公布過后，整套物業又因為其他引人矚目的數字，再次引起轟動。在給這套位于干德道39號的樓盤編制樓層號碼時，恒基沒有遵循傳統的一二三遞增的方式。比如，39樓上面就是60樓。最頂三層的號碼，分別是66樓，68樓和88樓。

    在拉斯維加斯，像7這樣的幸運數字很受歡迎。圖為2007年7月7日，很多情侶在曼德勒海灣酒店排隊等待舉行婚禮。這侵犯了一些人的秩序感。周日（10月25日）抗議高房價的過程中，一些香港民主黨立法會議員對這種牽強附會的編號方案表達了不滿。劉慧卿說，你可以把底樓叫做88樓，但沒有意義。你說你住88樓，人們都以為你住88樓，而不是10樓什么的。

    數字命理學（Numerology）相信，某些數字在表示數量之外，還有更多的意義。很久以來，這種信念都被數學家打入另冊。根據數字的讀音或字母表中跟數字對應的字母，數字命理學家對某些數字的態度或褒或貶。這樣一種邏輯，讓頭腦中只有數理規律與屬性的數學家們覺得，自己要比數字命理學家高明。

    但很多數學家對于起初促使他們進入這個領域的那些數字，也存在一些愛憎。一些人也會出現數理邏輯上的矛盾，跟數字命理學家們的錯誤比起來，差別也不是那么大。

    《數字的秘密人生》（The Secret Lives of Numbers）設計者列文（Golan Levin）在電子郵件里寫道，有人認為，數字多少是純粹的、與迷信思維無涉，因為相比語詞，它們總要"客觀"些，但這樣的觀念沒有考慮到，每一個觀念，都是以富含情感與文化的各種信號所織成的錦緞的形式存在于我們的大腦中的�！稊底值拿孛苋松�》是一個互動項目，跟蹤1到100萬之間每一個整數的受歡迎程度。

    威廉姆斯學院（Williams College）數學家嘉里蒂（Thomas Garrity）對數字9一直有著一種特殊的喜愛。但數字51卻不在他的喜好之列。

    他回憶自己的數學之路說，這可能跟我小時候有關，當時我經常以為51應該是質數，雖然51=3×17.但他說，自己不會以自己的好惡來做決定，比如說是避開大樓里的第51樓。嘉里蒂教授說，我可以理解人們對某些數字的一些細微的非理性情感，不過我不能理解人們以這樣的情感為基礎來做真正的決定。

    但某些數字迷信還是被擴大化，特別是在涉及利潤的時候。當香港恒基為迎合西式口味省掉13樓時，拉斯維加斯一家賭場為迎合香港賭客，樓層編號也略過了40到59樓。

    恒基一位女發言人說，客戶不喜歡帶4的數字和不吉利的數字。這些數字有著更為豐富的蘊涵。

    恒基所以按照它的方式編制樓層號碼，是因為6和8能引起積極聯想，4會引起消極聯想。加州大學伯克利分校（University of California, Berkeley）名譽數學教授伍鴻熙（Hung-Hsi Wu）說，在粵語和普通話中，8讀起來像發財的"發".因為這個原因，北京奧運會開幕選在了2008年8月8日的晚上8點。而數字4聽起來很像"死",所以人們會不顧一切地避免。6也被認為是吉利數字。

    對6的偏愛和對4的排斥，影響了拉斯維加斯42層樓高的賭場曼德勒灣 （Mandalay Bay）的開發商。這里的頂層都被命名為60層，61層和62層，因為它略過了40到59.

    曼德勒灣業主美高梅金殿夢幻（MGM Mirage）發言人阿布謝（Gordon Absher）表示，這種決定緣于賭客被安排到這些樓層時可能有的一些觀念。他說，你可能會覺得，我們作為賭場想給你帶來厄運。

    同樣，希望減輕人們對13的恐懼的開發商，不能夠避免一幢樓層數目不低于13的大樓里存在第13樓。但他們可以通過命名來讓"13"消失。上世紀30年代，俄克拉荷馬城（Oklahoma City）的Skirvin酒店加蓋第13層的時候，這層樓被命名為14樓。這座酒店在1988年停止營業，2007年被希爾頓（Hilton）收購后重新開張和命名，不過頂層的編號仍然沒有變化。

    芝加哥（Chicago）22層樓的Marc Realty則把第13層樓命名為"14A",把第14層命名為"14B".這樣就沒有讓上面的樓層名不副實。

    Marc營銷協調人克爾奇（Dan Krc）說，這種安排讓上面的樓層高度以一種直觀的方式呈現。他說，"13恐懼癥"似乎正在消失，Marc物業中被標為13樓的樓層，入住率并不比其他樓層低。

    數字13引起的負面聯想，源自于耶穌遭背叛前夕"最后的晚餐"當中的就餐者人數。而一些人相信，這種聯想要追溯到史前時代──13是不能用十指或兩只腳數盡的最小數目（顯然腳趾頭不算）.

    但迪普奧大學 （Depauw University） 退休數學教授、《數字命理學》作者達德利（Underwood Dudley）表示，他無法對這些說法予以證實。達德利博士說，據我所知，必須有某個數字是不吉利的，而這個數字就是13.

    美國威斯康星州梅庫恩（Mequon, Wisc.）的數字命理學家凱（Beverly Kay）并不害怕13.不過她說，她為顧客的生日和姓名賦予意義的工作，與數學是相通的。凱女士說，這是科學。

    心理學家和歷史學家一般都試圖把這種信念跟人類的一種普遍傾向聯系起來，這種傾向就是在不存在類型和系統的地方尋找類型和系統。在極端情況下，數字的情感聯想可能會潛入強迫性的行為。在《數字的異想世界》（Strange Brains and Genius）一書中，皮寇弗（Clifford Pickover）深入研究了數字性強迫性紊亂的各種案例，發現這種紊亂可以跟任何數字發生聯系。電子學先驅臺斯拉（Nikola Tesla）每天要用18塊干凈毛巾，并對3的倍數顯示了強烈的偏好。

    數學家一般不會達到臺斯拉這樣的極端，他們認為，他們對所有數字是一視同仁的，而這把他們和數字命理學家們區別開來。

    例如加州大學伯克利分校教授里貝（Kenneth Ribet）就說，他把一些質數視為"朋友".其中一個是144,169,就像是12的平方跟了一個13的平方。另外一個比較容易記住的數字是1,234,567,891.

    里貝教授說，數學家并沒有怕見到或不愿見到的數字，因為我們對所有數字真的都很喜歡。他說，另一方面，我們當中一些人確實偏愛一些數字。