21653931 has 16 divisors (see below), whose sum is σ = 31560704. Its totient is φ = 13125024.

The previous prime is 21653927. The next prime is 21653941. The reversal of 21653931 is 13935612.

It is not a de Polignac number, because 21653931 - 2² = 21653927 is a prime.

It is a super-2 number, since 2×21653931² = 937785455505522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21653941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1531 + ... + 6756.

It is an arithmetic number, because the mean of its divisors is an integer number (1972544).

Almost surely, 2^21653931 is an apocalyptic number.

21653931 is a deficient number, since it is larger than the sum of its proper divisors (9906773).

21653931 is a wasteful number, since it uses less digits than its factorization.

21653931 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8370.

The product of its digits is 4860, while the sum is 30.

The square root of 21653931 is about 4653.3784501156. The cubic root of 21653931 is about 278.7269202740.

The spelling of 21653931 in words is "twenty-one million, six hundred fifty-three thousand, nine hundred thirty-one".