157561721 has 4 divisors (see below), whose sum is σ = 157623552. Its totient is φ = 157499892.

The previous prime is 157561711. The next prime is 157561759. The reversal of 157561721 is 127165751.

157561721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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: 127165751 = 31 ⋅4102121.

It is a cyclic number.

It is not a de Polignac number, because 157561721 - 2¹⁴ = 157545337 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (157561711) 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, 26921 + ... + 32246.

It is an arithmetic number, because the mean of its divisors is an integer number (39405888).

Almost surely, 2^157561721 is an apocalyptic number.

It is an amenable number.

157561721 is a deficient number, since it is larger than the sum of its proper divisors (61831).

157561721 is an equidigital number, since it uses as much as digits as its factorization.

157561721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 61830.

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

The square root of 157561721 is about 12552.3591806481. The cubic root of 157561721 is about 540.1116835757. Note that the first 3 decimals are identical.

The spelling of 157561721 in words is "one hundred fifty-seven million, five hundred sixty-one thousand, seven hundred twenty-one".