18615981 has 4 divisors (see below), whose sum is σ = 24821312. Its totient is φ = 12410652.

The previous prime is 18615979. The next prime is 18615983. The reversal of 18615981 is 18951681.

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 an interprime number because it is at equal distance from previous prime (18615979) and next prime (18615983).

It is not a de Polignac number, because 18615981 - 2¹ = 18615979 is a prime.

It is a super-2 number, since 2×18615981² = 693109497184722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18615983) 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, 3102661 + ... + 3102666.

It is an arithmetic number, because the mean of its divisors is an integer number (6205328).

Almost surely, 2^18615981 is an apocalyptic number.

It is an amenable number.

18615981 is a deficient number, since it is larger than the sum of its proper divisors (6205331).

18615981 is an equidigital number, since it uses as much as digits as its factorization.

18615981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6205330.

The product of its digits is 17280, while the sum is 39.

The square root of 18615981 is about 4314.6240855954. The cubic root of 18615981 is about 265.0301662586.

The spelling of 18615981 in words is "eighteen million, six hundred fifteen thousand, nine hundred eighty-one".