18561681 has 12 divisors (see below), whose sum is σ = 27435408. Its totient is φ = 12086424.

The previous prime is 18561677. The next prime is 18561691. The reversal of 18561681 is 18616581.

18561681 is a `hidden beast` number, since 18 + 561 + 6 + 81 = 666.

It is not a de Polignac number, because 18561681 - 2² = 18561677 is a prime.

It is a super-2 number, since 2×18561681² = 689072003091522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (18561691) 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, 23595 + ... + 24368.

It is an arithmetic number, because the mean of its divisors is an integer number (2286284).

Almost surely, 2^18561681 is an apocalyptic number.

It is an amenable number.

18561681 is a deficient number, since it is larger than the sum of its proper divisors (8873727).

18561681 is a wasteful number, since it uses less digits than its factorization.

18561681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 48012 (or 48009 counting only the distinct ones).

The product of its digits is 11520, while the sum is 36.

The square root of 18561681 is about 4308.3269374550. The cubic root of 18561681 is about 264.7722310110.

The spelling of 18561681 in words is "eighteen million, five hundred sixty-one thousand, six hundred eighty-one".