21137431 has 4 divisors (see below), whose sum is σ = 24157072. Its totient is φ = 18117792.

The previous prime is 21137429. The next prime is 21137447. The reversal of 21137431 is 13473112.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21137431 - 2¹ = 21137429 is a prime.

It is a super-2 number, since 2×21137431² = 893581978559522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21137461) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1509810 + ... + 1509823.

It is an arithmetic number, because the mean of its divisors is an integer number (6039268).

Almost surely, 2^21137431 is an apocalyptic number.

21137431 is a deficient number, since it is larger than the sum of its proper divisors (3019641).

21137431 is an equidigital number, since it uses as much as digits as its factorization.

21137431 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3019640.

The product of its digits is 504, while the sum is 22.

The square root of 21137431 is about 4597.5461933514. The cubic root of 21137431 is about 276.4929534832.

The spelling of 21137431 in words is "twenty-one million, one hundred thirty-seven thousand, four hundred thirty-one".