21531658172 has 12 divisors (see below), whose sum is σ = 37702308336. Its totient is φ = 10759570080.

The previous prime is 21531658171. The next prime is 21531658199. The reversal of 21531658172 is 27185613512.

It is a happy number.

It is a super-2 number, since 2×21531658172² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531658171) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1557008 + ... + 1570775.

It is an arithmetic number, because the mean of its divisors is an integer number (3141859028).

Almost surely, 2^21531658172 is an apocalyptic number.

It is an amenable number.

21531658172 is a deficient number, since it is larger than the sum of its proper divisors (16170650164).

21531658172 is a wasteful number, since it uses less digits than its factorization.

21531658172 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3129508 (or 3129506 counting only the distinct ones).

The product of its digits is 100800, while the sum is 41.

The spelling of 21531658172 in words is "twenty-one billion, five hundred thirty-one million, six hundred fifty-eight thousand, one hundred seventy-two".