21631891 has 8 divisors (see below), whose sum is σ = 23053824. Its totient is φ = 20250120.

The previous prime is 21631879. The next prime is 21631903. The reversal of 21631891 is 19813612.

It is an interprime number because it is at equal distance from previous prime (21631879) and next prime (21631903).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21631891 - 2¹¹ = 21629843 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21631391) 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 7 ways as a sum of consecutive naturals, for example, 8925 + ... + 11086.

It is an arithmetic number, because the mean of its divisors is an integer number (2881728).

Almost surely, 2^21631891 is an apocalyptic number.

21631891 is a deficient number, since it is larger than the sum of its proper divisors (1421933).

21631891 is a wasteful number, since it uses less digits than its factorization.

21631891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20081.

The product of its digits is 2592, while the sum is 31.

The square root of 21631891 is about 4651.0096753286. The cubic root of 21631891 is about 278.6323227200.

It can be divided in two parts, 21631 and 891, that added together give a palindrome (22522).

The spelling of 21631891 in words is "twenty-one million, six hundred thirty-one thousand, eight hundred ninety-one".