21661056899744 has 48 divisors (see below), whose sum is σ = 45382954350888. Its totient is φ = 10141695148032.

The previous prime is 21661056899717. The next prime is 21661056899749. The reversal of 21661056899744 is 44799865016612.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 21176379168400 + 484677731344 = 4601780^2 + 696188^2 .

It is a Harshad number since it is a multiple of its sum of digits (68).

It is not an unprimeable number, because it can be changed into a prime (21661056899749) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 100954049 + ... + 101168384.

Almost surely, 2^{21661056899744} is an apocalyptic number.

It is an amenable number.

21661056899744 is an abundant number, since it is smaller than the sum of its proper divisors (23721897451144).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21661056899744 is a wasteful number, since it uses less digits than its factorization.

21661056899744 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 202122657 (or 202122649 counting only the distinct ones).

The product of its (nonzero) digits is 156764160, while the sum is 68.

The spelling of 21661056899744 in words is "twenty-one trillion, six hundred sixty-one billion, fifty-six million, eight hundred ninety-nine thousand, seven hundred forty-four".