21365971857 has 16 divisors (see below), whose sum is σ = 31819023360. Its totient is φ = 14169402000.

The previous prime is 21365971853. The next prime is 21365971871. The reversal of 21365971857 is 75817956312.

21365971857 is a `hidden beast` number, since 2 + 1 + 36 + 597 + 18 + 5 + 7 = 666.

It is not a de Polignac number, because 21365971857 - 2² = 21365971853 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21365971853) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2066394 + ... + 2076707.

It is an arithmetic number, because the mean of its divisors is an integer number (1988688960).

Almost surely, 2^21365971857 is an apocalyptic number.

21365971857 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21365971857 is a deficient number, since it is larger than the sum of its proper divisors (10453051503).

21365971857 is a wasteful number, since it uses less digits than its factorization.

21365971857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4143301 (or 4143295 counting only the distinct ones).

The product of its digits is 3175200, while the sum is 54.

The spelling of 21365971857 in words is "twenty-one billion, three hundred sixty-five million, nine hundred seventy-one thousand, eight hundred fifty-seven".