21312979 has 2 divisors, whose sum is σ = 21312980. Its totient is φ = 21312978.

The previous prime is 21312961. The next prime is 21313001. The reversal of 21312979 is 97921312.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21312979 - 2¹⁷ = 21181907 is a prime.

It is not a weakly prime, because it can be changed into another prime (21312959) 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 as a sum of consecutive naturals, namely, 10656489 + 10656490.

It is an arithmetic number, because the mean of its divisors is an integer number (10656490).

Almost surely, 2^21312979 is an apocalyptic number.

21312979 is a deficient number, since it is larger than the sum of its proper divisors (1).

21312979 is an equidigital number, since it uses as much as digits as its factorization.

21312979 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6804, while the sum is 34.

The square root of 21312979 is about 4616.5982064719. The cubic root of 21312979 is about 277.2562760071.

The spelling of 21312979 in words is "twenty-one million, three hundred twelve thousand, nine hundred seventy-nine".