21661225465664 has 28 divisors (see below), whose sum is σ = 43572816132324. Its totient is φ = 10682248172544.

The previous prime is 21661225465661. The next prime is 21661225465697. The reversal of 21661225465664 is 46656452216612.

It can be written as a sum of positive squares in 2 ways, for example, as 8682498705664 + 12978726760000 = 2946608^2 + 3602600^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661225465661) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2318191547 + ... + 2318200890.

Almost surely, 2^{21661225465664} is an apocalyptic number.

It is an amenable number.

21661225465664 is an abundant number, since it is smaller than the sum of its proper divisors (21911590666660).

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

21661225465664 is an equidigital number, since it uses as much as digits as its factorization.

21661225465664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4636392522 (or 4636392512 counting only the distinct ones).

The product of its digits is 24883200, while the sum is 56.

The spelling of 21661225465664 in words is "twenty-one trillion, six hundred sixty-one billion, two hundred twenty-five million, four hundred sixty-five thousand, six hundred sixty-four".