21857115231 has 24 divisors (see below), whose sum is σ = 36283178880. Its totient is φ = 12419998416.

The previous prime is 21857115229. The next prime is 21857115233. The reversal of 21857115231 is 13251175812.

21857115231 is a `hidden beast` number, since 2 + 1 + 8 + 571 + 1 + 52 + 31 = 666.

It is an interprime number because it is at equal distance from previous prime (21857115229) and next prime (21857115233).

It is not a de Polignac number, because 21857115231 - 2¹ = 21857115229 is a prime.

It is a super-2 number, since 2×21857115231² (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 (21857115233) 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, 957825 + ... + 980378.

It is an arithmetic number, because the mean of its divisors is an integer number (1511799120).

Almost surely, 2^21857115231 is an apocalyptic number.

21857115231 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21857115231 is a deficient number, since it is larger than the sum of its proper divisors (14426063649).

21857115231 is a wasteful number, since it uses less digits than its factorization.

21857115231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1938395 (or 1938392 counting only the distinct ones).

The product of its digits is 16800, while the sum is 36.

The spelling of 21857115231 in words is "twenty-one billion, eight hundred fifty-seven million, one hundred fifteen thousand, two hundred thirty-one".