21590991 has 24 divisors (see below), whose sum is σ = 32207760. Its totient is φ = 13931136.

The previous prime is 21590983. The next prime is 21590999. The reversal of 21590991 is 19909512.

It is an interprime number because it is at equal distance from previous prime (21590983) and next prime (21590999).

It is not a de Polignac number, because 21590991 - 2³ = 21590983 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21590999) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 38485 + ... + 39041.

It is an arithmetic number, because the mean of its divisors is an integer number (1341990).

Almost surely, 2^21590991 is an apocalyptic number.

21590991 is a deficient number, since it is larger than the sum of its proper divisors (10616769).

21590991 is a wasteful number, since it uses less digits than its factorization.

21590991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 695 (or 692 counting only the distinct ones).

The product of its (nonzero) digits is 7290, while the sum is 36.

The square root of 21590991 is about 4646.6107002847. The cubic root of 21590991 is about 278.4566060457.

It can be divided in two parts, 215909 and 91, that added together give a cube (216000 = 60³).

The spelling of 21590991 in words is "twenty-one million, five hundred ninety thousand, nine hundred ninety-one".