21564931 has 2 divisors, whose sum is σ = 21564932. Its totient is φ = 21564930.

The previous prime is 21564929. The next prime is 21564941. The reversal of 21564931 is 13946512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21564931 - 2¹ = 21564929 is a prime.

It is a super-2 number, since 2×21564931² = 930092498069522, which contains 22 as substring.

Together with 21564929, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 21564893 and 21564902.

It is not a weakly prime, because it can be changed into another prime (21564941) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10782465 + 10782466.

It is an arithmetic number, because the mean of its divisors is an integer number (10782466).

Almost surely, 2^21564931 is an apocalyptic number.

21564931 is a deficient number, since it is larger than the sum of its proper divisors (1).

21564931 is an equidigital number, since it uses as much as digits as its factorization.

21564931 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6480, while the sum is 31.

The square root of 21564931 is about 4643.8056591550. The cubic root of 21564931 is about 278.3445299698.

The spelling of 21564931 in words is "twenty-one million, five hundred sixty-four thousand, nine hundred thirty-one".