21604993 has 2 divisors, whose sum is σ = 21604994. Its totient is φ = 21604992.

The previous prime is 21604987. The next prime is 21604997. The reversal of 21604993 is 39940612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21603904 + 1089 = 4648^2 + 33^2 .

It is a cyclic number.

It is not a de Polignac number, because 21604993 - 2⁹ = 21604481 is a prime.

It is not a weakly prime, because it can be changed into another prime (21604997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802496 + 10802497.

It is an arithmetic number, because the mean of its divisors is an integer number (10802497).

Almost surely, 2^21604993 is an apocalyptic number.

It is an amenable number.

21604993 is a deficient number, since it is larger than the sum of its proper divisors (1).

21604993 is an equidigital number, since it uses as much as digits as its factorization.

21604993 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 11664, while the sum is 34.

The square root of 21604993 is about 4648.1171456838. The cubic root of 21604993 is about 278.5167871163.

The spelling of 21604993 in words is "twenty-one million, six hundred four thousand, nine hundred ninety-three".