# 133

This number is a composite.

The reversal of 133 is prime. Note that 133.335 is the Dewey Decimal classification for 'numerology'. If you reverse it, and add: 133.335 + 533.331, you'll discover the beast number, repeated! [Gardner]

133 is the smallest positive integer, n, for which the integer 10*n* + 5 is divisible by both 3 and 5 and for which none of the integers 10*n* + 1, 10*n* + 3, 10*n* + 7, and 10*n* + 9 are prime. [Litman]

The sum of the first three squares of semiprimes is itself a semiprime, and this is the first such sum with this property: 133 = 4^2 + 6^2 + 9^2 = 7 * 19. [Post]

The last 133 digits of 131^132 is prime. [Gupta]

(There are 4 curios for this number that have not yet been approved by an editor.)

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