21115431 has 8 divisors (see below), whose sum is σ = 31282160. Its totient is φ = 14076936.

The previous prime is 21115429. The next prime is 21115439. The reversal of 21115431 is 13451112.

It is not a de Polignac number, because 21115431 - 2¹ = 21115429 is a prime.

It is a super-2 number, since 2×21115431² = 891722852631522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21115439) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 391000 + ... + 391053.

It is an arithmetic number, because the mean of its divisors is an integer number (3910270).

Almost surely, 2^21115431 is an apocalyptic number.

21115431 is a deficient number, since it is larger than the sum of its proper divisors (10166729).

21115431 is an equidigital number, since it uses as much as digits as its factorization.

21115431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 782062 (or 782056 counting only the distinct ones).

The product of its digits is 120, while the sum is 18.

The square root of 21115431 is about 4595.1529898361. The cubic root of 21115431 is about 276.3969948565.

Adding to 21115431 its reverse (13451112), we get a palindrome (34566543).

The spelling of 21115431 in words is "twenty-one million, one hundred fifteen thousand, four hundred thirty-one".