21108431 has 2 divisors, whose sum is σ = 21108432. Its totient is φ = 21108430.

The previous prime is 21108419. The next prime is 21108497. The reversal of 21108431 is 13480112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21108431 - 2¹⁰ = 21107407 is a prime.

It is a super-2 number, since 2×21108431² = 891131718563522, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21108631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10554215 + 10554216.

It is an arithmetic number, because the mean of its divisors is an integer number (10554216).

Almost surely, 2^21108431 is an apocalyptic number.

21108431 is a deficient number, since it is larger than the sum of its proper divisors (1).

21108431 is an equidigital number, since it uses as much as digits as its factorization.

21108431 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 192, while the sum is 20.

The square root of 21108431 is about 4594.3912545625. The cubic root of 21108431 is about 276.3664485891.

Adding to 21108431 its reverse (13480112), we get a palindrome (34588543).

The spelling of 21108431 in words is "twenty-one million, one hundred eight thousand, four hundred thirty-one".