21565718620 has 192 divisors, whose sum is σ = 50426449920. Its totient is φ = 7721505792.

The previous prime is 21565718593. The next prime is 21565718651. The reversal of 21565718620 is 2681756512.

It is a Harshad number since it is a multiple of its sum of digits (43).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 57816754 + ... + 57817126.

It is an arithmetic number, because the mean of its divisors is an integer number (262637760).

Almost surely, 2^21565718620 is an apocalyptic number.

21565718620 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 21565718620, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25213224960).

21565718620 is an abundant number, since it is smaller than the sum of its proper divisors (28860731300).

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

21565718620 is a wasteful number, since it uses less digits than its factorization.

21565718620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 564 (or 562 counting only the distinct ones).

The product of its (nonzero) digits is 201600, while the sum is 43.

The spelling of 21565718620 in words is "twenty-one billion, five hundred sixty-five million, seven hundred eighteen thousand, six hundred twenty".