21688380857 has 12 divisors (see below), whose sum is σ = 25673088420. Its totient is φ = 18200038560.

The previous prime is 21688380841. The next prime is 21688380869. The reversal of 21688380857 is 75808388612.

It can be written as a sum of positive squares in 2 ways, for example, as 2429602681 + 19258778176 = 49291^2 + 138776^2 .

It is not a de Polignac number, because 21688380857 - 2⁴ = 21688380841 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21688380827) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6892382 + ... + 6895527.

It is an arithmetic number, because the mean of its divisors is an integer number (2139424035).

Almost surely, 2^21688380857 is an apocalyptic number.

It is an amenable number.

21688380857 is a deficient number, since it is larger than the sum of its proper divisors (3984707563).

21688380857 is a wasteful number, since it uses less digits than its factorization.

21688380857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13787944 (or 13787933 counting only the distinct ones).

The product of its (nonzero) digits is 5160960, while the sum is 56.

The spelling of 21688380857 in words is "twenty-one billion, six hundred eighty-eight million, three hundred eighty thousand, eight hundred fifty-seven".