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4 is the first number to be [[a ]]semiprime number]]. The next is 6. 

4 is the first number to be [[a ]]semiprime number]]. The next is 6. 




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4 is associated with bad luck in Eastern numerology because the Chinese word for "four" sounds similar to the word for "death."

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== In googology == 

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In Greekbased numbernaming systems, 4 is associated with prefix "'''tetra'''", and with prefix "'''quad'''" in Latin systems. 




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It is possible to test for divisibility by 4 in base 10 by looking at last 2 digits of the number. If the 2digit number is divisible by 4, then the whole number is.

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4 can be named "'''fztwo'''", "'''fugatwo'''", "'''megafugatwo'''", "'''boogatwo'''", "'''twoplaton'''", "'''gartwo'''", "'''bartwo'''", "'''trartwo'''", "'''quadrartwo'''", "'''quintartwo'''", "'''sextartwo'''", "'''septartwo'''", "'''octartwo'''", "'''nonartwo'''". 
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Ignoring weekdays, the Julian calendar repeats every '''4''' years. 

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Its Roman numeral is most commonly IV, but on clock faces, IIII is also used. 

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== In [[googology]] == 

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Some googologisms based on 4 are [[supertet]], [[quadroogol]] and [[googolquadriplex]]. 4 can be thought as [[zero]]th term of sequence defining Graham's number: \(g_0\) = 4. 

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In Greekbased number naming systems, 4 is associated with prefix tetra, and with prefix quad in Latin systems. 

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4 can be named gartwo, fztwo, fugatwo, megafugatwo, boogatwo, or twoplaton with the [[gar]], [[fz]], [[fuga]], [[megafuga]], [[booga]], and [[platon]] prefixes respectively. 






Testing if a number is a multiple of 4 can be done by seeing if the last two digits make a multiple of 4. So 57368 is a multiple of 4 since 68 = 4*17. 

Testing if a number is a multiple of 4 can be done by seeing if the last two digits make a multiple of 4. So 57368 is a multiple of 4 since 68 = 4*17. 