81807561 has 12 divisors (see below), whose sum is σ = 128909040. Its totient is φ = 49580280.

The previous prime is 81807547. The next prime is 81807563. The reversal of 81807561 is 16570818.

It is not a de Polignac number, because 81807561 - 2⁶ = 81807497 is a prime.

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 not an unprimeable number, because it can be changed into a prime (81807563) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 413071 + ... + 413268.

It is an arithmetic number, because the mean of its divisors is an integer number (10742420).

Almost surely, 2^81807561 is an apocalyptic number.

It is an amenable number.

81807561 is a deficient number, since it is larger than the sum of its proper divisors (47101479).

81807561 is a wasteful number, since it uses less digits than its factorization.

81807561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 826356 (or 826353 counting only the distinct ones).

The product of its (nonzero) digits is 13440, while the sum is 36.

The square root of 81807561 is about 9044.7532304646. The cubic root of 81807561 is about 434.1080255916.

The spelling of 81807561 in words is "eighty-one million, eight hundred seven thousand, five hundred sixty-one".