191021257 has 6 divisors (see below), whose sum is σ = 222208458. Its totient is φ = 163732464.

The previous prime is 191021219. The next prime is 191021267. The reversal of 191021257 is 752120191.

It can be written as a sum of positive squares in only one way, i.e., 185749641 + 5271616 = 13629^2 + 2296^2 .

It is a de Polignac number, because none of the positive numbers 2^k-191021257 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (191021267) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1949148 + ... + 1949245.

It is an arithmetic number, because the mean of its divisors is an integer number (37034743).

Almost surely, 2^191021257 is an apocalyptic number.

It is an amenable number.

191021257 is a deficient number, since it is larger than the sum of its proper divisors (31187201).

191021257 is an equidigital number, since it uses as much as digits as its factorization.

191021257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3898407 (or 3898400 counting only the distinct ones).

The product of its (nonzero) digits is 1260, while the sum is 28.

The square root of 191021257 is about 13821.0439909581. The cubic root of 191021257 is about 575.9178857111.

The spelling of 191021257 in words is "one hundred ninety-one million, twenty-one thousand, two hundred fifty-seven".