21655640006520 has 256 divisors, whose sum is σ = 71050996800000. Its totient is φ = 5247923890176.

The previous prime is 21655640006489. The next prime is 21655640006527. The reversal of 21655640006520 is 2560004655612.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21655640006527) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 177518506 + ... + 177640454.

It is an arithmetic number, because the mean of its divisors is an integer number (277542956250).

Almost surely, 2^{21655640006520} is an apocalyptic number.

21655640006520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21655640006520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35525498400000).

21655640006520 is an abundant number, since it is smaller than the sum of its proper divisors (49395356793480).

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

21655640006520 is a wasteful number, since it uses less digits than its factorization.

21655640006520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 123742 (or 123738 counting only the distinct ones).

The product of its (nonzero) digits is 432000, while the sum is 42.

The spelling of 21655640006520 in words is "twenty-one trillion, six hundred fifty-five billion, six hundred forty million, six thousand, five hundred twenty".