1516391721 has 24 divisors (see below), whose sum is σ = 2497589640. Its totient is φ = 878270976.

The previous prime is 1516391719. The next prime is 1516391731. The reversal of 1516391721 is 1271936151.

It is a happy number.

1516391721 is a `hidden beast` number, since 1 + 5 + 1 + 639 + 17 + 2 + 1 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 68121 + 1516323600 = 261^2 + 38940^2 .

It is not a de Polignac number, because 1516391721 - 2¹ = 1516391719 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1516391711) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 379206 + ... + 383183.

It is an arithmetic number, because the mean of its divisors is an integer number (104066235).

Almost surely, 2^1516391721 is an apocalyptic number.

It is an amenable number.

1516391721 is a deficient number, since it is larger than the sum of its proper divisors (981197919).

1516391721 is a wasteful number, since it uses less digits than its factorization.

1516391721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 762425 (or 762422 counting only the distinct ones).

The product of its digits is 11340, while the sum is 36.

The square root of 1516391721 is about 38940.8746820099. The cubic root of 1516391721 is about 1148.8688868200.

The spelling of 1516391721 in words is "one billion, five hundred sixteen million, three hundred ninety-one thousand, seven hundred twenty-one".