21957979 has 2 divisors, whose sum is σ = 21957980. Its totient is φ = 21957978.

The previous prime is 21957973. The next prime is 21957989. The reversal of 21957979 is 97975912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21957979 - 2⁷ = 21957851 is a prime.

It is not a weakly prime, because it can be changed into another prime (21957973) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10978989 + 10978990.

It is an arithmetic number, because the mean of its divisors is an integer number (10978990).

Almost surely, 2^21957979 is an apocalyptic number.

21957979 is a deficient number, since it is larger than the sum of its proper divisors (1).

21957979 is an equidigital number, since it uses as much as digits as its factorization.

21957979 is an evil number, because the sum of its binary digits is even.

The product of its digits is 357210, while the sum is 49.

The square root of 21957979 is about 4685.9341651372. The cubic root of 21957979 is about 280.0254186108.

The spelling of 21957979 in words is "twenty-one million, nine hundred fifty-seven thousand, nine hundred seventy-nine".