21631591 has 2 divisors, whose sum is σ = 21631592. Its totient is φ = 21631590.

The previous prime is 21631573. The next prime is 21631607. The reversal of 21631591 is 19513612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21631591 - 2¹⁷ = 21500519 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21631501) 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 as a sum of consecutive naturals, namely, 10815795 + 10815796.

It is an arithmetic number, because the mean of its divisors is an integer number (10815796).

Almost surely, 2^21631591 is an apocalyptic number.

21631591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21631591 is an equidigital number, since it uses as much as digits as its factorization.

21631591 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1620, while the sum is 28.

The square root of 21631591 is about 4650.9774241551. The cubic root of 21631591 is about 278.6310346513.

It can be divided in two parts, 21631 and 591, that added together give a palindrome (22222).

The spelling of 21631591 in words is "twenty-one million, six hundred thirty-one thousand, five hundred ninety-one".