21515997672 has 96 divisors (see below), whose sum is σ = 62917381800. Its totient is φ = 6603176448.

The previous prime is 21515997661. The next prime is 21515997707. The reversal of 21515997672 is 27679951512.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 17791824996 + 3724172676 = 133386^2 + 61026^2 .

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 334558 + ... + 393650.

Almost surely, 2^21515997672 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 21515997672, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31458690900).

21515997672 is an abundant number, since it is smaller than the sum of its proper divisors (41401384128).

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

21515997672 is a wasteful number, since it uses less digits than its factorization.

21515997672 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59507 (or 59500 counting only the distinct ones).

The product of its digits is 2381400, while the sum is 54.

The spelling of 21515997672 in words is "twenty-one billion, five hundred fifteen million, nine hundred ninety-seven thousand, six hundred seventy-two".