1557105721 has 4 divisors (see below), whose sum is σ = 1576816000. Its totient is φ = 1537395444.

The previous prime is 1557105713. The next prime is 1557105731. The reversal of 1557105721 is 1275017551.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1275017551 = 47 ⋅27128033.

It is a cyclic number.

It is not a de Polignac number, because 1557105721 - 2³ = 1557105713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1557105731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9855021 + ... + 9855178.

It is an arithmetic number, because the mean of its divisors is an integer number (394204000).

Almost surely, 2^1557105721 is an apocalyptic number.

It is an amenable number.

1557105721 is a deficient number, since it is larger than the sum of its proper divisors (19710279).

1557105721 is an equidigital number, since it uses as much as digits as its factorization.

1557105721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19710278.

The product of its (nonzero) digits is 12250, while the sum is 34.

The square root of 1557105721 is about 39460.1789276227. The cubic root of 1557105721 is about 1159.0603074001.

The spelling of 1557105721 in words is "one billion, five hundred fifty-seven million, one hundred five thousand, seven hundred twenty-one".