1516120721 has 4 divisors (see below), whose sum is σ = 1536889572. Its totient is φ = 1495351872.

The previous prime is 1516120709. The next prime is 1516120733. The reversal of 1516120721 is 1270216151.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1270216151 = 8231 ⋅154321.

It is an interprime number because it is at equal distance from previous prime (1516120709) and next prime (1516120733).

It can be written as a sum of positive squares in 2 ways, for example, as 555120721 + 961000000 = 23561^2 + 31000^2 .

It is a cyclic number.

It is not a de Polignac number, because 1516120721 - 2²² = 1511926417 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1516120321) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10384316 + ... + 10384461.

It is an arithmetic number, because the mean of its divisors is an integer number (384222393).

Almost surely, 2^1516120721 is an apocalyptic number.

It is an amenable number.

1516120721 is a deficient number, since it is larger than the sum of its proper divisors (20768851).

1516120721 is an equidigital number, since it uses as much as digits as its factorization.

1516120721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20768850.

The product of its (nonzero) digits is 840, while the sum is 26.

The square root of 1516120721 is about 38937.3948923140. The cubic root of 1516120721 is about 1148.8004431998.

Adding to 1516120721 its reverse (1270216151), we get a palindrome (2786336872).

The spelling of 1516120721 in words is "one billion, five hundred sixteen million, one hundred twenty thousand, seven hundred twenty-one".