21515569920 has 864 divisors, whose sum is σ = 88308747072. Its totient is φ = 4968677376.

The previous prime is 21515569891. The next prime is 21515569939. The reversal of 21515569920 is 2996551512.

21515569920 is a `hidden beast` number, since 2 + 1 + 5 + 1 + 556 + 9 + 92 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (864).

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 95 ways as a sum of consecutive naturals, for example, 68739684 + ... + 68739996.

It is an arithmetic number, because the mean of its divisors is an integer number (102209198).

Almost surely, 2^21515569920 is an apocalyptic number.

21515569920 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 21515569920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (44154373536).

21515569920 is an abundant number, since it is smaller than the sum of its proper divisors (66793177152).

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

21515569920 is a wasteful number, since it uses less digits than its factorization.

21515569920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 379 (or 353 counting only the distinct ones).

The product of its (nonzero) digits is 243000, while the sum is 45.

The spelling of 21515569920 in words is "twenty-one billion, five hundred fifteen million, five hundred sixty-nine thousand, nine hundred twenty".