21565244736 has 672 divisors, whose sum is σ = 79849472000. Its totient is φ = 5583790080.

The previous prime is 21565244731. The next prime is 21565244737. The reversal of 21565244736 is 63744256512.

21565244736 is a `hidden beast` number, since 2 + 1 + 56 + 524 + 4 + 73 + 6 = 666.

It is a tau number, because it is divible by the number of its divisors (672).

It is a junction number, because it is equal to n+sod(n) for n = 21565244691 and 21565244700.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21565244731) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 108367965 + ... + 108368163.

Almost surely, 2^21565244736 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21565244736, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39924736000).

21565244736 is an abundant number, since it is smaller than the sum of its proper divisors (58284227264).

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

21565244736 is a wasteful number, since it uses less digits than its factorization.

21565244736 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 292 (or 259 counting only the distinct ones).

The product of its digits is 1209600, while the sum is 45.

The spelling of 21565244736 in words is "twenty-one billion, five hundred sixty-five million, two hundred forty-four thousand, seven hundred thirty-six".