21515122431 has 24 divisors (see below), whose sum is σ = 33933805776. Its totient is φ = 13027472640.

The previous prime is 21515122381. The next prime is 21515122441. The reversal of 21515122431 is 13422151512.

It is a happy number.

21515122431 is a `hidden beast` number, since 21 + 515 + 122 + 4 + 3 + 1 = 666.

It is not a de Polignac number, because 21515122431 - 2¹⁸ = 21514860287 is a prime.

It is a super-2 number, since 2×21515122431² (a number of 21 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21515122395 and 21515122404.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21515122441) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 8791 + ... + 207623.

It is an arithmetic number, because the mean of its divisors is an integer number (1413908574).

Almost surely, 2^21515122431 is an apocalyptic number.

21515122431 is a deficient number, since it is larger than the sum of its proper divisors (12418683345).

21515122431 is a wasteful number, since it uses less digits than its factorization.

21515122431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 199943 (or 199940 counting only the distinct ones).

The product of its digits is 2400, while the sum is 27.

Adding to 21515122431 its reverse (13422151512), we get a palindrome (34937273943).

The spelling of 21515122431 in words is "twenty-one billion, five hundred fifteen million, one hundred twenty-two thousand, four hundred thirty-one".