21521715560 has 64 divisors (see below), whose sum is σ = 49280400000. Its totient is φ = 8456626432.

The previous prime is 21521715557. The next prime is 21521715563. The reversal of 21521715560 is 6551712512.

It is an interprime number because it is at equal distance from previous prime (21521715557) and next prime (21521715563).

It is a super-2 number, since 2×21521715560² (a number of 21 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21521715560.

It is not an unprimeable number, because it can be changed into a prime (21521715563) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4597301 + ... + 4601979.

It is an arithmetic number, because the mean of its divisors is an integer number (770006250).

Almost surely, 2^21521715560 is an apocalyptic number.

21521715560 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 21521715560, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24640200000).

21521715560 is an abundant number, since it is smaller than the sum of its proper divisors (27758684440).

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

21521715560 is a wasteful number, since it uses less digits than its factorization.

21521715560 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6698 (or 6694 counting only the distinct ones).

The product of its (nonzero) digits is 21000, while the sum is 35.

The spelling of 21521715560 in words is "twenty-one billion, five hundred twenty-one million, seven hundred fifteen thousand, five hundred sixty".