21564979 has 2 divisors, whose sum is σ = 21564980. Its totient is φ = 21564978.

The previous prime is 21564953. The next prime is 21564989. The reversal of 21564979 is 97946512.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21564979 is a prime.

It is not a weakly prime, because it can be changed into another prime (21564929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10782489 + 10782490.

It is an arithmetic number, because the mean of its divisors is an integer number (10782490).

Almost surely, 2^21564979 is an apocalyptic number.

21564979 is a deficient number, since it is larger than the sum of its proper divisors (1).

21564979 is an equidigital number, since it uses as much as digits as its factorization.

21564979 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 136080, while the sum is 43.

The square root of 21564979 is about 4643.8108273271. The cubic root of 21564979 is about 278.3447364861.

The spelling of 21564979 in words is "twenty-one million, five hundred sixty-four thousand, nine hundred seventy-nine".