81209664 has 42 divisors (see below), whose sum is σ = 232774490. Its totient is φ = 27069696.

The previous prime is 81209659. The next prime is 81209693. The reversal of 81209664 is 46690218.

It can be written as a sum of positive squares in only one way, i.e., 67371264 + 13838400 = 8208^2 + 3720^2 .

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 69919 + ... + 71070.

Almost surely, 2^81209664 is an apocalyptic number.

It is an amenable number.

81209664 is an abundant number, since it is smaller than the sum of its proper divisors (151564826).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81209664 is a wasteful number, since it uses less digits than its factorization.

81209664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 141007 (or 140994 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 36.

The square root of 81209664 is about 9011.6404721893. The cubic root of 81209664 is about 433.0478677388.

The spelling of 81209664 in words is "eighty-one million, two hundred nine thousand, six hundred sixty-four".