81515681 has 16 divisors (see below), whose sum is σ = 92749440. Its totient is φ = 71020800.

The previous prime is 81515653. The next prime is 81515683. The reversal of 81515681 is 18651518.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81515681 is a prime.

It is a super-2 number, since 2×81515681² = 13289612497787522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81515683) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 98636 + ... + 99458.

It is an arithmetic number, because the mean of its divisors is an integer number (5796840).

Almost surely, 2^81515681 is an apocalyptic number.

81515681 is the 5213-rd octagonal number.

It is an amenable number.

81515681 is a deficient number, since it is larger than the sum of its proper divisors (11233759).

81515681 is a wasteful number, since it uses less digits than its factorization.

81515681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1256.

The product of its digits is 9600, while the sum is 35.

The square root of 81515681 is about 9028.6034911275. The cubic root of 81515681 is about 433.5911278016.

The spelling of 81515681 in words is "eighty-one million, five hundred fifteen thousand, six hundred eighty-one".