20391157 has 2 divisors, whose sum is σ = 20391158. Its totient is φ = 20391156.

The previous prime is 20391139. The next prime is 20391169. The reversal of 20391157 is 75119302.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16573041 + 3818116 = 4071^2 + 1954^2 .

It is a cyclic number.

It is not a de Polignac number, because 20391157 - 2¹⁵ = 20358389 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20391197) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10195578 + 10195579.

It is an arithmetic number, because the mean of its divisors is an integer number (10195579).

Almost surely, 2^20391157 is an apocalyptic number.

It is an amenable number.

20391157 is a deficient number, since it is larger than the sum of its proper divisors (1).

20391157 is an equidigital number, since it uses as much as digits as its factorization.

20391157 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1890, while the sum is 28.

The square root of 20391157 is about 4515.6568735899. The cubic root of 20391157 is about 273.1999545898.

The spelling of 20391157 in words is "twenty million, three hundred ninety-one thousand, one hundred fifty-seven".