21500431 has 2 divisors, whose sum is σ = 21500432. Its totient is φ = 21500430.

The previous prime is 21500429. The next prime is 21500443. The reversal of 21500431 is 13400512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21500431 - 2¹ = 21500429 is a prime.

It is a super-2 number, since 2×21500431² = 924537066371522, which contains 22 as substring.

Together with 21500429, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21500491) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10750215 + 10750216.

It is an arithmetic number, because the mean of its divisors is an integer number (10750216).

Almost surely, 2^21500431 is an apocalyptic number.

21500431 is a deficient number, since it is larger than the sum of its proper divisors (1).

21500431 is an equidigital number, since it uses as much as digits as its factorization.

21500431 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21500431 is about 4636.8557234402. The cubic root of 21500431 is about 278.0667463907.

Adding to 21500431 its reverse (13400512), we get a palindrome (34900943).

The spelling of 21500431 in words is "twenty-one million, five hundred thousand, four hundred thirty-one".