21662591 has 2 divisors, whose sum is σ = 21662592. Its totient is φ = 21662590.

The previous prime is 21662579. The next prime is 21662609. The reversal of 21662591 is 19526612.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21662591 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21662791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10831295 + 10831296.

It is an arithmetic number, because the mean of its divisors is an integer number (10831296).

Almost surely, 2^21662591 is an apocalyptic number.

21662591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21662591 is an equidigital number, since it uses as much as digits as its factorization.

21662591 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6480, while the sum is 32.

The square root of 21662591 is about 4654.3088638379. The cubic root of 21662591 is about 278.7640721646.

The spelling of 21662591 in words is "twenty-one million, six hundred sixty-two thousand, five hundred ninety-one".