21556979 has 2 divisors, whose sum is σ = 21556980. Its totient is φ = 21556978.

The previous prime is 21556961. The next prime is 21556987. The reversal of 21556979 is 97965512.

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-21556979 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21556999) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778489 + 10778490.

It is an arithmetic number, because the mean of its divisors is an integer number (10778490).

Almost surely, 2^21556979 is an apocalyptic number.

21556979 is a deficient number, since it is larger than the sum of its proper divisors (1).

21556979 is an equidigital number, since it uses as much as digits as its factorization.

21556979 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 170100, while the sum is 44.

The square root of 21556979 is about 4642.9493858969. The cubic root of 21556979 is about 278.3103128757.

The spelling of 21556979 in words is "twenty-one million, five hundred fifty-six thousand, nine hundred seventy-nine".