81506565257 has 4 divisors (see below), whose sum is σ = 87776301060. Its totient is φ = 75236829456.

The previous prime is 81506565253. The next prime is 81506565269. The reversal of 81506565257 is 75256560518.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 34410621001 + 47095944256 = 185501^2 + 217016^2 .

It is a cyclic number.

It is not a de Polignac number, because 81506565257 - 2² = 81506565253 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81506565253) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3134867882 + ... + 3134867907.

It is an arithmetic number, because the mean of its divisors is an integer number (21944075265).

Almost surely, 2^81506565257 is an apocalyptic number.

It is an amenable number.

81506565257 is a deficient number, since it is larger than the sum of its proper divisors (6269735803).

81506565257 is a wasteful number, since it uses less digits than its factorization.

81506565257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6269735802.

The product of its (nonzero) digits is 2520000, while the sum is 50.

The spelling of 81506565257 in words is "eighty-one billion, five hundred six million, five hundred sixty-five thousand, two hundred fifty-seven".