21605217504 has 96 divisors (see below), whose sum is σ = 61108346880. Its totient is φ = 6644270592.

The previous prime is 21605217461. The next prime is 21605217523. The reversal of 21605217504 is 40571250612.

It is a tau number, because it is divible by the number of its divisors (96).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3390129 + ... + 3396495.

It is an arithmetic number, because the mean of its divisors is an integer number (636545280).

Almost surely, 2^21605217504 is an apocalyptic number.

21605217504 is a gapful number since it is divisible by the number (24) 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 21605217504, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30554173440).

21605217504 is an abundant number, since it is smaller than the sum of its proper divisors (39503129376).

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

21605217504 is a wasteful number, since it uses less digits than its factorization.

21605217504 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9112 (or 9104 counting only the distinct ones).

The product of its (nonzero) digits is 16800, while the sum is 33.

The spelling of 21605217504 in words is "twenty-one billion, six hundred five million, two hundred seventeen thousand, five hundred four".