1575216721 has 27 divisors (see below), whose sum is σ = 1771240347. Its totient is φ = 1400227920.

The previous prime is 1575216691. The next prime is 1575216737. The reversal of 1575216721 is 1276125751.

The square root of 1575216721 is 39689.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 233020225 + 1342196496 = 15265^2 + 36636^2 .

It is not a de Polignac number, because 1575216721 - 2⁵ = 1575216689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1575216781) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 22186116 + ... + 22186186.

Almost surely, 2^1575216721 is an apocalyptic number.

1575216721 is the 39689-th square number.

1575216721 is the 19845-th centered octagonal number.

It is an amenable number.

1575216721 is a deficient number, since it is larger than the sum of its proper divisors (196023626).

1575216721 is an frugal number, since it uses more digits than its factorization.

1575216721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 254 (or 127 counting only the distinct ones).

The product of its digits is 29400, while the sum is 37.

The cubic root of 1575216721 is about 1163.5367486286.

The spelling of 1575216721 in words is "one billion, five hundred seventy-five million, two hundred sixteen thousand, seven hundred twenty-one".