21105660681 has 36 divisors (see below), whose sum is σ = 35807633472. Its totient is φ = 11943260784.

The previous prime is 21105660679. The next prime is 21105660749. The reversal of 21105660681 is 18606650112.

21105660681 is a `hidden beast` number, since 2 + 1 + 10 + 566 + 0 + 6 + 81 = 666.

It is not a de Polignac number, because 21105660681 - 2¹ = 21105660679 is a prime.

It is a super-2 number, since 2×21105660681² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21105664681) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 186901 + ... + 277746.

Almost surely, 2^21105660681 is an apocalyptic number.

21105660681 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21105660681 is a deficient number, since it is larger than the sum of its proper divisors (14701972791).

21105660681 is a wasteful number, since it uses less digits than its factorization.

21105660681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 464770 (or 464760 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 36.

The spelling of 21105660681 in words is "twenty-one billion, one hundred five million, six hundred sixty thousand, six hundred eighty-one".