1520138577721 has 27 divisors (see below), whose sum is σ = 1589168670957. Its totient is φ = 1454078939040.

The previous prime is 1520138577677. The next prime is 1520138577761. The reversal of 1520138577721 is 1277758310251.

The square root of 1520138577721 is 1232939.

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

It can be written as a sum of positive squares in 4 ways, for example, as 23763764025 + 1496374813696 = 154155^2 + 1223264^2 .

It is not a de Polignac number, because 1520138577721 - 2²⁵ = 1520105023289 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1520138577761) 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, 2809867711 + ... + 2809868251.

Almost surely, 2^{1520138577721} is an apocalyptic number.

1520138577721 is the 1232939-th square number.

1520138577721 is the 616470-th centered octagonal number.

It is an amenable number.

1520138577721 is a deficient number, since it is larger than the sum of its proper divisors (69030093236).

1520138577721 is an frugal number, since it uses more digits than its factorization.

1520138577721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1274 (or 637 counting only the distinct ones).

The product of its (nonzero) digits is 823200, while the sum is 49.

Multiplying 1520138577721 by its sum of digits (49), we get a square (74486790308329 = 8630573²).

The spelling of 1520138577721 in words is "one trillion, five hundred twenty billion, one hundred thirty-eight million, five hundred seventy-seven thousand, seven hundred twenty-one".