18171981 has 12 divisors (see below), whose sum is σ = 26504608. Its totient is φ = 11996424.

The previous prime is 18171977. The next prime is 18171991. The reversal of 18171981 is 18917181.

It is a happy number.

It is not a de Polignac number, because 18171981 - 2² = 18171977 is a prime.

It is a super-2 number, since 2×18171981² = 660441786928722, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18171971) 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, 8875 + ... + 10728.

Almost surely, 2^18171981 is an apocalyptic number.

It is an amenable number.

18171981 is a deficient number, since it is larger than the sum of its proper divisors (8332627).

18171981 is a wasteful number, since it uses less digits than its factorization.

18171981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19712 (or 19709 counting only the distinct ones).

The product of its digits is 4032, while the sum is 36.

The square root of 18171981 is about 4262.8606592287. The cubic root of 18171981 is about 262.9061576361.

The spelling of 18171981 in words is "eighteen million, one hundred seventy-one thousand, nine hundred eighty-one".