21431131 has 2 divisors, whose sum is σ = 21431132. Its totient is φ = 21431130.

The previous prime is 21431129. The next prime is 21431141. The reversal of 21431131 is 13113412.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21431131 - 2¹ = 21431129 is a prime.

It is a super-2 number, since 2×21431131² = 918586751878322, which contains 22 as substring.

Together with 21431129, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21431141) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10715565 + 10715566.

It is an arithmetic number, because the mean of its divisors is an integer number (10715566).

Almost surely, 2^21431131 is an apocalyptic number.

21431131 is a deficient number, since it is larger than the sum of its proper divisors (1).

21431131 is an equidigital number, since it uses as much as digits as its factorization.

21431131 is an evil number, because the sum of its binary digits is even.

The product of its digits is 72, while the sum is 16.

The square root of 21431131 is about 4629.3769559197. The cubic root of 21431131 is about 277.7676707374.

Adding to 21431131 its reverse (13113412), we get a palindrome (34544543).

The spelling of 21431131 in words is "twenty-one million, four hundred thirty-one thousand, one hundred thirty-one".