21121979 has 2 divisors, whose sum is σ = 21121980. Its totient is φ = 21121978.

The previous prime is 21121967. The next prime is 21121999. The reversal of 21121979 is 97912112.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21121979 is a prime.

It is a super-2 number, since 2×21121979² = 892275993752882, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21121909) 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, 10560989 + 10560990.

It is an arithmetic number, because the mean of its divisors is an integer number (10560990).

Almost surely, 2^21121979 is an apocalyptic number.

21121979 is a deficient number, since it is larger than the sum of its proper divisors (1).

21121979 is an equidigital number, since it uses as much as digits as its factorization.

21121979 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2268, while the sum is 32.

The square root of 21121979 is about 4595.8654244875. The cubic root of 21121979 is about 276.4255625972.

The spelling of 21121979 in words is "twenty-one million, one hundred twenty-one thousand, nine hundred seventy-nine".