21615766560 has 216 divisors, whose sum is σ = 78359597316. Its totient is φ = 5425029120.

The previous prime is 21615766553. The next prime is 21615766603. The reversal of 21615766560 is 6566751612.

21615766560 is a `hidden beast` number, since 2 + 1 + 6 + 15 + 76 + 6 + 560 = 666.

It can be written as a sum of positive squares in 6 ways, for example, as 9126363024 + 12489403536 = 95532^2 + 111756^2 .

It is a Harshad number since it is a multiple of its sum of digits (45).

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 390190 + ... + 442130.

Almost surely, 2^21615766560 is an apocalyptic number.

21615766560 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 21615766560, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39179798658).

21615766560 is an abundant number, since it is smaller than the sum of its proper divisors (56743830756).

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

21615766560 is a wasteful number, since it uses less digits than its factorization.

21615766560 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51996 (or 51968 counting only the distinct ones).

The product of its (nonzero) digits is 453600, while the sum is 45.

The spelling of 21615766560 in words is "twenty-one billion, six hundred fifteen million, seven hundred sixty-six thousand, five hundred sixty".