21664051 has 2 divisors, whose sum is σ = 21664052. Its totient is φ = 21664050.

The previous prime is 21664037. The next prime is 21664063. The reversal of 21664051 is 15046612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21664051 - 2⁷ = 21663923 is a prime.

It is a super-2 number, since 2×21664051² = 938662211461202, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21664081) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10832025 + 10832026.

It is an arithmetic number, because the mean of its divisors is an integer number (10832026).

Almost surely, 2^21664051 is an apocalyptic number.

21664051 is a deficient number, since it is larger than the sum of its proper divisors (1).

21664051 is an equidigital number, since it uses as much as digits as its factorization.

21664051 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21664051 is about 4654.4657051052. The cubic root of 21664051 is about 278.7703346719.

The spelling of 21664051 in words is "twenty-one million, six hundred sixty-four thousand, fifty-one".