251721157 has 2 divisors, whose sum is σ = 251721158. Its totient is φ = 251721156.

The previous prime is 251721149. The next prime is 251721161. The reversal of 251721157 is 751127152.

251721157 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 245893761 + 5827396 = 15681^2 + 2414^2 .

It is a cyclic number.

It is not a de Polignac number, because 251721157 - 2³ = 251721149 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (251721137) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125860578 + 125860579.

It is an arithmetic number, because the mean of its divisors is an integer number (125860579).

Almost surely, 2^251721157 is an apocalyptic number.

It is an amenable number.

251721157 is a deficient number, since it is larger than the sum of its proper divisors (1).

251721157 is an equidigital number, since it uses as much as digits as its factorization.

251721157 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4900, while the sum is 31.

The square root of 251721157 is about 15865.7227065142. The cubic root of 251721157 is about 631.4029012092.

The spelling of 251721157 in words is "two hundred fifty-one million, seven hundred twenty-one thousand, one hundred fifty-seven".