1557610721 has 2 divisors, whose sum is σ = 1557610722. Its totient is φ = 1557610720.

The previous prime is 1557610631. The next prime is 1557610723. The reversal of 1557610721 is 1270167551.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 847974400 + 709636321 = 29120^2 + 26639^2 .

It is an emirp because it is prime and its reverse (1270167551) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1557610721 is a prime.

It is a Sophie Germain prime.

Together with 1557610723, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (1557610723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 778805360 + 778805361.

It is an arithmetic number, because the mean of its divisors is an integer number (778805361).

Almost surely, 2^1557610721 is an apocalyptic number.

It is an amenable number.

1557610721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1557610721 is an equidigital number, since it uses as much as digits as its factorization.

1557610721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 14700, while the sum is 35.

The square root of 1557610721 is about 39466.5772648199. The cubic root of 1557610721 is about 1159.1855958720.

The spelling of 1557610721 in words is "one billion, five hundred fifty-seven million, six hundred ten thousand, seven hundred twenty-one".