21664501 has 2 divisors, whose sum is σ = 21664502. Its totient is φ = 21664500.

The previous prime is 21664483. The next prime is 21664507. The reversal of 21664501 is 10546612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12215025 + 9449476 = 3495^2 + 3074^2 .

It is a cyclic number.

It is not a de Polignac number, because 21664501 - 2⁷ = 21664373 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21664507) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10832250 + 10832251.

It is an arithmetic number, because the mean of its divisors is an integer number (10832251).

Almost surely, 2^21664501 is an apocalyptic number.

It is an amenable number.

21664501 is a deficient number, since it is larger than the sum of its proper divisors (1).

21664501 is an equidigital number, since it uses as much as digits as its factorization.

21664501 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 21664501 is about 4654.5140455261. The cubic root of 21664501 is about 278.7722648400.

The spelling of 21664501 in words is "twenty-one million, six hundred sixty-four thousand, five hundred one".