21505681960 has 192 divisors, whose sum is σ = 57654904320. Its totient is φ = 7071805440.

The previous prime is 21505681919. The next prime is 21505681961. The reversal of 21505681960 is 6918650512.

It is not an unprimeable number, because it can be changed into a prime (21505681961) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 63814912 + ... + 63815248.

It is an arithmetic number, because the mean of its divisors is an integer number (300285960).

Almost surely, 2^21505681960 is an apocalyptic number.

21505681960 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 21505681960, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28827452160).

21505681960 is an abundant number, since it is smaller than the sum of its proper divisors (36149222360).

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

21505681960 is a wasteful number, since it uses less digits than its factorization.

21505681960 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 684 (or 651 counting only the distinct ones).

The product of its (nonzero) digits is 129600, while the sum is 43.

The spelling of 21505681960 in words is "twenty-one billion, five hundred five million, six hundred eighty-one thousand, nine hundred sixty".