81564981 has 4 divisors (see below), whose sum is σ = 108753312. Its totient is φ = 54376652.

The previous prime is 81564943. The next prime is 81565007. The reversal of 81564981 is 18946518.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81564981 - 2¹¹ = 81562933 is a prime.

It is a super-2 number, since 2×81564981² = 13305692251060722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81564911) 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, 13594161 + ... + 13594166.

It is an arithmetic number, because the mean of its divisors is an integer number (27188328).

Almost surely, 2^81564981 is an apocalyptic number.

It is an amenable number.

81564981 is a deficient number, since it is larger than the sum of its proper divisors (27188331).

81564981 is a wasteful number, since it uses less digits than its factorization.

81564981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27188330.

The product of its digits is 69120, while the sum is 42.

The square root of 81564981 is about 9031.3332902734. Note that the first 3 decimals coincide. The cubic root of 81564981 is about 433.6785209446.

The spelling of 81564981 in words is "eighty-one million, five hundred sixty-four thousand, nine hundred eighty-one".