157821721 has 4 divisors (see below), whose sum is σ = 157991092. Its totient is φ = 157652352.

The previous prime is 157821709. The next prime is 157821731. The reversal of 157821721 is 127128751.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9834496 + 147987225 = 3136^2 + 12165^2 .

It is a cyclic number.

It is not a de Polignac number, because 157821721 - 2⁵ = 157821689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (157821731) 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, 83280 + ... + 85153.

It is an arithmetic number, because the mean of its divisors is an integer number (39497773).

Almost surely, 2^157821721 is an apocalyptic number.

It is an amenable number.

157821721 is a deficient number, since it is larger than the sum of its proper divisors (169371).

157821721 is an equidigital number, since it uses as much as digits as its factorization.

157821721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 169370.

The product of its digits is 7840, while the sum is 34.

The square root of 157821721 is about 12562.7115305574. The cubic root of 157821721 is about 540.4086082025.

The spelling of 157821721 in words is "one hundred fifty-seven million, eight hundred twenty-one thousand, seven hundred twenty-one".