21902591 has 4 divisors (see below), whose sum is σ = 21964992. Its totient is φ = 21840192.

The previous prime is 21902581. The next prime is 21902593. The reversal of 21902591 is 19520912.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21902591 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21902593) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 30671 + ... + 31376.

It is an arithmetic number, because the mean of its divisors is an integer number (5491248).

Almost surely, 2^21902591 is an apocalyptic number.

21902591 is a deficient number, since it is larger than the sum of its proper divisors (62401).

21902591 is an equidigital number, since it uses as much as digits as its factorization.

21902591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 62400.

The product of its (nonzero) digits is 1620, while the sum is 29.

The square root of 21902591 is about 4680.0204059384. The cubic root of 21902591 is about 279.7897699153.

The spelling of 21902591 in words is "twenty-one million, nine hundred two thousand, five hundred ninety-one".