21631291 has 18 divisors (see below), whose sum is σ = 25288620. Its totient is φ = 18437760.

The previous prime is 21631289. The next prime is 21631297. The reversal of 21631291 is 19213612.

It is not a de Polignac number, because 21631291 - 2¹ = 21631289 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21631297) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 222955 + ... + 223051.

Almost surely, 2^21631291 is an apocalyptic number.

21631291 is a deficient number, since it is larger than the sum of its proper divisors (3657329).

21631291 is an equidigital number, since it uses as much as digits as its factorization.

21631291 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 235 (or 127 counting only the distinct ones).

The product of its digits is 648, while the sum is 25.

The square root of 21631291 is about 4650.9451727579. The cubic root of 21631291 is about 278.6297465707.

The spelling of 21631291 in words is "twenty-one million, six hundred thirty-one thousand, two hundred ninety-one".