81521307 has 48 divisors (see below), whose sum is σ = 144069120. Its totient is φ = 43358976.

The previous prime is 81521299. The next prime is 81521309. The reversal of 81521307 is 70312518.

It is not a de Polignac number, because 81521307 - 2³ = 81521299 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81521309) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 109944 + ... + 110682.

It is an arithmetic number, because the mean of its divisors is an integer number (3001440).

Almost surely, 2^81521307 is an apocalyptic number.

81521307 is a deficient number, since it is larger than the sum of its proper divisors (62547813).

81521307 is a wasteful number, since it uses less digits than its factorization.

81521307 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 872 (or 869 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 81521307 is about 9028.9150511011. The cubic root of 81521307 is about 433.6011026822.

It can be divided in two parts, 815 and 21307, that added together give a palindrome (22122).

The spelling of 81521307 in words is "eighty-one million, five hundred twenty-one thousand, three hundred seven".