21181986 has 40 divisors (see below), whose sum is σ = 54246720. Its totient is φ = 6051672.

The previous prime is 21181961. The next prime is 21181997. The reversal of 21181986 is 68918112.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21181986.

It is an unprimeable number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 8206 + ... + 10473.

It is an arithmetic number, because the mean of its divisors is an integer number (1356168).

Almost surely, 2^21181986 is an apocalyptic number.

21181986 is an abundant number, since it is smaller than the sum of its proper divisors (33064734).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21181986 is a wasteful number, since it uses less digits than its factorization.

21181986 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18700 (or 18691 counting only the distinct ones).

The product of its digits is 6912, while the sum is 36.

The square root of 21181986 is about 4602.3891621635. The cubic root of 21181986 is about 276.6870877332.

The spelling of 21181986 in words is "twenty-one million, one hundred eighty-one thousand, nine hundred eighty-six".