21784725531 has 12 divisors (see below), whose sum is σ = 33317815752. Its totient is φ = 13668847296.

The previous prime is 21784725493. The next prime is 21784725581. The reversal of 21784725531 is 13552748712.

21784725531 is a `hidden beast` number, since 2 + 1 + 78 + 47 + 2 + 5 + 531 = 666.

It is a de Polignac number, because none of the positive numbers 2^k-21784725531 is a prime.

It is a super-2 number, since 2×21784725531² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21784725581) 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, 71191761 + ... + 71192066.

It is an arithmetic number, because the mean of its divisors is an integer number (2776484646).

Almost surely, 2^21784725531 is an apocalyptic number.

21784725531 is a deficient number, since it is larger than the sum of its proper divisors (11533090221).

21784725531 is a wasteful number, since it uses less digits than its factorization.

21784725531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 142383850 (or 142383847 counting only the distinct ones).

The product of its digits is 470400, while the sum is 45.

The spelling of 21784725531 in words is "twenty-one billion, seven hundred eighty-four million, seven hundred twenty-five thousand, five hundred thirty-one".