21691431 has 12 divisors (see below), whose sum is σ = 31656352. Its totient is φ = 14311296.

The previous prime is 21691421. The next prime is 21691441. The reversal of 21691431 is 13419612.

It is an interprime number because it is at equal distance from previous prime (21691421) and next prime (21691441).

It is not a de Polignac number, because 21691431 - 2⁹ = 21690919 is a prime.

It is a super-2 number, since 2×21691431² = 941036357655522, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21691395 and 21691404.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21691421) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 11551 + ... + 13296.

Almost surely, 2^21691431 is an apocalyptic number.

21691431 is a deficient number, since it is larger than the sum of its proper divisors (9964921).

21691431 is a wasteful number, since it uses less digits than its factorization.

21691431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24950 (or 24947 counting only the distinct ones).

The product of its digits is 1296, while the sum is 27.

The square root of 21691431 is about 4657.4060376995. The cubic root of 21691431 is about 278.8877260512.

It can be divided in two parts, 21691 and 431, that added together give a palindrome (22122).

The spelling of 21691431 in words is "twenty-one million, six hundred ninety-one thousand, four hundred thirty-one".