21656039 has 2 divisors, whose sum is σ = 21656040. Its totient is φ = 21656038.

The previous prime is 21656023. The next prime is 21656057. The reversal of 21656039 is 93065612.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21656039 - 2⁴ = 21656023 is a prime.

It is a Sophie Germain prime.

It is a junction number, because it is equal to n+sod(n) for n = 21655996 and 21656014.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21656099) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10828019 + 10828020.

It is an arithmetic number, because the mean of its divisors is an integer number (10828020).

Almost surely, 2^21656039 is an apocalyptic number.

21656039 is a deficient number, since it is larger than the sum of its proper divisors (1).

21656039 is an equidigital number, since it uses as much as digits as its factorization.

21656039 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 9720, while the sum is 32.

The square root of 21656039 is about 4653.6049467053. The cubic root of 21656039 is about 278.7359646254.

It can be divided in two parts, 2165603 and 9, that added together give a palindrome (2165612).

The spelling of 21656039 in words is "twenty-one million, six hundred fifty-six thousand, thirty-nine".