21507891768 has 160 divisors (see below), whose sum is σ = 69584747760. Its totient is φ = 6134123520.

The previous prime is 21507891709. The next prime is 21507891799. The reversal of 21507891768 is 86719870512.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 32430 + ... + 209922.

Almost surely, 2^21507891768 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21507891768, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34792373880).

21507891768 is an abundant number, since it is smaller than the sum of its proper divisors (48076855992).

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

21507891768 is a wasteful number, since it uses less digits than its factorization.

21507891768 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 177539 (or 177526 counting only the distinct ones).

The product of its (nonzero) digits is 1693440, while the sum is 54.

The spelling of 21507891768 in words is "twenty-one billion, five hundred seven million, eight hundred ninety-one thousand, seven hundred sixty-eight".