21694638681 has 27 divisors (see below), whose sum is σ = 32473718589. Its totient is φ = 13956116832.

The previous prime is 21694638671. The next prime is 21694638701. The reversal of 21694638681 is 18683649612.

The square root of 21694638681 is 147291.

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

21694638681 is a `hidden beast` number, since 21 + 6 + 9 + 463 + 86 + 81 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 198387225 + 21496251456 = 14085^2 + 146616^2 .

It is not a de Polignac number, because 21694638681 - 2²¹ = 21692541529 is a prime.

It is a super-2 number, since 2×21694638681² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21694638631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 12813471 + ... + 12815163.

Almost surely, 2^21694638681 is an apocalyptic number.

21694638681 is the 147291-st square number.

21694638681 is the 73646-th centered octagonal number.

It is an amenable number.

21694638681 is a deficient number, since it is larger than the sum of its proper divisors (10779079908).

21694638681 is an frugal number, since it uses more digits than its factorization.

21694638681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3450 (or 1725 counting only the distinct ones).

The product of its digits is 2985984, while the sum is 54.

The spelling of 21694638681 in words is "twenty-one billion, six hundred ninety-four million, six hundred thirty-eight thousand, six hundred eighty-one".