21995991 has 6 divisors (see below), whose sum is σ = 31772000. Its totient is φ = 14663988.

The previous prime is 21995951. The next prime is 21995993. The reversal of 21995991 is 19959912.

It is not a de Polignac number, because 21995991 - 2¹³ = 21987799 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21995993) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1221991 + ... + 1222008.

Almost surely, 2^21995991 is an apocalyptic number.

21995991 is a deficient number, since it is larger than the sum of its proper divisors (9776009).

21995991 is a wasteful number, since it uses less digits than its factorization.

21995991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2444005 (or 2444002 counting only the distinct ones).

The product of its digits is 65610, while the sum is 45.

The square root of 21995991 is about 4689.9883795165. The cubic root of 21995991 is about 280.1869117654.

The spelling of 21995991 in words is "twenty-one million, nine hundred ninety-five thousand, nine hundred ninety-one".