21721015680 has 768 divisors, whose sum is σ = 87518154240. Its totient is φ = 4485611520.

The previous prime is 21721015639. The next prime is 21721015717. The reversal of 21721015680 is 8651012712.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 165809215 + ... + 165809345.

It is an arithmetic number, because the mean of its divisors is an integer number (113955930).

Almost surely, 2^21721015680 is an apocalyptic number.

21721015680 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 21721015680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (43759077120).

21721015680 is an abundant number, since it is smaller than the sum of its proper divisors (65797138560).

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

21721015680 is a wasteful number, since it uses less digits than its factorization.

21721015680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 259 (or 234 counting only the distinct ones).

The product of its (nonzero) digits is 6720, while the sum is 33.

The spelling of 21721015680 in words is "twenty-one billion, seven hundred twenty-one million, fifteen thousand, six hundred eighty".