81531609 has 16 divisors (see below), whose sum is σ = 118217088. Its totient is φ = 49773312.

The previous prime is 81531601. The next prime is 81531623. The reversal of 81531609 is 90613518.

It is not a de Polignac number, because 81531609 - 2³ = 81531601 is a prime.

It is a super-2 number, since 2×81531609² = 13294806532257762, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 81531609.

It is not an unprimeable number, because it can be changed into a prime (81531601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 19717 + ... + 23490.

It is an arithmetic number, because the mean of its divisors is an integer number (7388568).

Almost surely, 2^81531609 is an apocalyptic number.

It is an amenable number.

81531609 is a deficient number, since it is larger than the sum of its proper divisors (36685479).

81531609 is a wasteful number, since it uses less digits than its factorization.

81531609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43264.

The product of its (nonzero) digits is 6480, while the sum is 33.

The square root of 81531609 is about 9029.4855335174. The cubic root of 81531609 is about 433.6193669069.

The spelling of 81531609 in words is "eighty-one million, five hundred thirty-one thousand, six hundred nine".