1521721764 has 18 divisors (see below), whose sum is σ = 3846574550. Its totient is φ = 507240576.

The previous prime is 1521721753. The next prime is 1521721823. The reversal of 1521721764 is 4671271251.

1521721764 is a `hidden beast` number, since 1 + 521 + 72 + 1 + 7 + 64 = 666.

It can be written as a sum of positive squares in only one way, i.e., 822542400 + 699179364 = 28680^2 + 26442^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 42270049 = 1521721764 / (1 + 5 + 2 + 1 + 7 + 2 + 1 + 7 + 6 + 4).

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 21134989 + ... + 21135060.

Almost surely, 2^1521721764 is an apocalyptic number.

It is an amenable number.

1521721764 is an abundant number, since it is smaller than the sum of its proper divisors (2324852786).

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

1521721764 is a wasteful number, since it uses less digits than its factorization.

1521721764 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42270059 (or 42270054 counting only the distinct ones).

The product of its digits is 23520, while the sum is 36.

The square root of 1521721764 is about 39009.2522871177. The cubic root of 1521721764 is about 1150.2133854821.

The spelling of 1521721764 in words is "one billion, five hundred twenty-one million, seven hundred twenty-one thousand, seven hundred sixty-four".