21815581131 has 12 divisors (see below), whose sum is σ = 31524616240. Its totient is φ = 14537618640.

The previous prime is 21815581129. The next prime is 21815581157. The reversal of 21815581131 is 13118551812.

21815581131 is a `hidden beast` number, since 21 + 81 + 558 + 1 + 1 + 3 + 1 = 666.

It is not a de Polignac number, because 21815581131 - 2¹ = 21815581129 is a prime.

It is a super-3 number, since 3×21815581131³ (a number of 32 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21815581031) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 485815 + ... + 528816.

Almost surely, 2^21815581131 is an apocalyptic number.

21815581131 is a deficient number, since it is larger than the sum of its proper divisors (9709035109).

21815581131 is a wasteful number, since it uses less digits than its factorization.

21815581131 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1017026 (or 1017023 counting only the distinct ones).

The product of its digits is 9600, while the sum is 36.

The spelling of 21815581131 in words is "twenty-one billion, eight hundred fifteen million, five hundred eighty-one thousand, one hundred thirty-one".