21247979 has 2 divisors, whose sum is σ = 21247980. Its totient is φ = 21247978.

The previous prime is 21247937. The next prime is 21247987. The reversal of 21247979 is 97974212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21247979 - 2¹⁶ = 21182443 is a prime.

It is a super-2 number, since 2×21247979² = 902953223168882, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21247999) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10623989 + 10623990.

It is an arithmetic number, because the mean of its divisors is an integer number (10623990).

Almost surely, 2^21247979 is an apocalyptic number.

21247979 is a deficient number, since it is larger than the sum of its proper divisors (1).

21247979 is an equidigital number, since it uses as much as digits as its factorization.

21247979 is an evil number, because the sum of its binary digits is even.

The product of its digits is 63504, while the sum is 41.

The square root of 21247979 is about 4609.5530152066. The cubic root of 21247979 is about 276.9741316579.

The spelling of 21247979 in words is "twenty-one million, two hundred forty-seven thousand, nine hundred seventy-nine".