21604393 has 2 divisors, whose sum is σ = 21604394. Its totient is φ = 21604392.

The previous prime is 21604381. The next prime is 21604397. The reversal of 21604393 is 39340612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11888704 + 9715689 = 3448^2 + 3117^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21604393 is a prime.

It is not a weakly prime, because it can be changed into another prime (21604397) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802196 + 10802197.

It is an arithmetic number, because the mean of its divisors is an integer number (10802197).

Almost surely, 2^21604393 is an apocalyptic number.

It is an amenable number.

21604393 is a deficient number, since it is larger than the sum of its proper divisors (1).

21604393 is an equidigital number, since it uses as much as digits as its factorization.

21604393 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3888, while the sum is 28.

The square root of 21604393 is about 4648.0526029726. The cubic root of 21604393 is about 278.5142088293.

The spelling of 21604393 in words is "twenty-one million, six hundred four thousand, three hundred ninety-three".