21664373 has 2 divisors, whose sum is σ = 21664374. Its totient is φ = 21664372.

The previous prime is 21664361. The next prime is 21664417. The reversal of 21664373 is 37346612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13410244 + 8254129 = 3662^2 + 2873^2 .

It is a cyclic number.

It is not a de Polignac number, because 21664373 - 2⁸ = 21664117 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21664343) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10832186 + 10832187.

It is an arithmetic number, because the mean of its divisors is an integer number (10832187).

Almost surely, 2^21664373 is an apocalyptic number.

It is an amenable number.

21664373 is a deficient number, since it is larger than the sum of its proper divisors (1).

21664373 is an equidigital number, since it uses as much as digits as its factorization.

21664373 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18144, while the sum is 32.

The square root of 21664373 is about 4654.5002954130. The cubic root of 21664373 is about 278.7717158171.

The spelling of 21664373 in words is "twenty-one million, six hundred sixty-four thousand, three hundred seventy-three".