21517581680 has 240 divisors, whose sum is σ = 59342362560. Its totient is φ = 7233859584.

The previous prime is 21517581677. The next prime is 21517581721. The reversal of 21517581680 is 8618571512.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 55314926 + ... + 55315314.

It is an arithmetic number, because the mean of its divisors is an integer number (247259844).

Almost surely, 2^21517581680 is an apocalyptic number.

21517581680 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 21517581680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29671181280).

21517581680 is an abundant number, since it is smaller than the sum of its proper divisors (37824780880).

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

21517581680 is a wasteful number, since it uses less digits than its factorization.

21517581680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 656 (or 643 counting only the distinct ones).

The product of its (nonzero) digits is 134400, while the sum is 44.

The spelling of 21517581680 in words is "twenty-one billion, five hundred seventeen million, five hundred eighty-one thousand, six hundred eighty".