69

69 (sixty-nine) is the natural number following 68 and preceding 70. In mathematics 69 is: a lucky number. the twentieth semiprime (3.23) and the seventh of the form (3.q) where q is a higher prime. the aliquot sum of sixty-nine is 27 within the aliquot sequence (69,27,13,1,0) and is the third composite number in the 13-aliquot tree; following (27,35). a Blum integer, since the two factors of 69 are both Gaussian primes. the sum of the sums of the divisors of the first 9 positive integers. a strobogrammatic number. a centered tetrahedral number. Because 69 has an odd number of 1s in its binary representation, it is sometimes called an "odious number."