21308431 has 2 divisors, whose sum is σ = 21308432. Its totient is φ = 21308430.

The previous prime is 21308393. The next prime is 21308467. The reversal of 21308431 is 13480312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21308431 - 2⁷ = 21308303 is a prime.

It is a super-2 number, since 2×21308431² = 908098463363522, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21308471) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10654215 + 10654216.

It is an arithmetic number, because the mean of its divisors is an integer number (10654216).

Almost surely, 2^21308431 is an apocalyptic number.

21308431 is a deficient number, since it is larger than the sum of its proper divisors (1).

21308431 is an equidigital number, since it uses as much as digits as its factorization.

21308431 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 576, while the sum is 22.

The square root of 21308431 is about 4616.1056097104. The cubic root of 21308431 is about 277.2365532638.

Adding to 21308431 its reverse (13480312), we get a palindrome (34788743).

The spelling of 21308431 in words is "twenty-one million, three hundred eight thousand, four hundred thirty-one".