157721209 has 4 divisors (see below), whose sum is σ = 159717760. Its totient is φ = 155724660.

The previous prime is 157721203. The next prime is 157721233. The reversal of 157721209 is 902127751.

157721209 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: 902127751 = 7 ⋅128875393.

It is a cyclic number.

It is not a de Polignac number, because 157721209 - 2⁵ = 157721177 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (157721203) 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, 998157 + ... + 998314.

It is an arithmetic number, because the mean of its divisors is an integer number (39929440).

Almost surely, 2^157721209 is an apocalyptic number.

It is an amenable number.

157721209 is a deficient number, since it is larger than the sum of its proper divisors (1996551).

157721209 is an equidigital number, since it uses as much as digits as its factorization.

157721209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1996550.

The product of its (nonzero) digits is 8820, while the sum is 34.

The square root of 157721209 is about 12558.7104831667. The cubic root of 157721209 is about 540.2938604038.

The spelling of 157721209 in words is "one hundred fifty-seven million, seven hundred twenty-one thousand, two hundred nine".