21688477953921 has 27 divisors (see below), whose sum is σ = 32009501483011. Its totient is φ = 14150918865264.

The previous prime is 21688477953899. The next prime is 21688477954057. The reversal of 21688477953921 is 12935977488612.

The square root of 21688477953921 is 4657089.

It is a perfect power (a square), and thus also a powerful number.

21688477953921 is a `hidden beast` number, since 2 + 1 + 6 + 8 + 84 + 7 + 7 + 9 + 539 + 2 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 11818081521 + 21676659872400 = 108711^2 + 4655820^2 .

It is not a de Polignac number, because 21688477953921 - 2⁹ = 21688477953409 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21688477953921.

It is not an unprimeable number, because it can be changed into a prime (21688477953421) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 656633035 + ... + 656666063.

Almost surely, 2^{21688477953921} is an apocalyptic number.

21688477953921 is the 4657089-th square number.

21688477953921 is the 2328545-th centered octagonal number.

It is an amenable number.

21688477953921 is a deficient number, since it is larger than the sum of its proper divisors (10321023529090).

21688477953921 is an frugal number, since it uses more digits than its factorization.

21688477953921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 66158 (or 33079 counting only the distinct ones).

The product of its digits is 365783040, while the sum is 72.

The spelling of 21688477953921 in words is "twenty-one trillion, six hundred eighty-eight billion, four hundred seventy-seven million, nine hundred fifty-three thousand, nine hundred twenty-one".