21213431 has 2 divisors, whose sum is σ = 21213432. Its totient is φ = 21213430.

The previous prime is 21213427. The next prime is 21213449. The reversal of 21213431 is 13431212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21213431 - 2² = 21213427 is a prime.

It is a super-2 number, since 2×21213431² = 900019309583522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21213461) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606715 + 10606716.

It is an arithmetic number, because the mean of its divisors is an integer number (10606716).

Almost surely, 2^21213431 is an apocalyptic number.

21213431 is a deficient number, since it is larger than the sum of its proper divisors (1).

21213431 is an equidigital number, since it uses as much as digits as its factorization.

21213431 is an evil number, because the sum of its binary digits is even.

The product of its digits is 144, while the sum is 17.

The square root of 21213431 is about 4605.8040557540. The cubic root of 21213431 is about 276.8239355200.

Adding to 21213431 its reverse (13431212), we get a palindrome (34644643).

The spelling of 21213431 in words is "twenty-one million, two hundred thirteen thousand, four hundred thirty-one".