991638157 has 2 divisors, whose sum is σ = 991638158. Its totient is φ = 991638156.

The previous prime is 991638133. The next prime is 991638161. The reversal of 991638157 is 751836199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 660798436 + 330839721 = 25706^2 + 18189^2 .

It is an emirp because it is prime and its reverse (751836199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991638157 - 2⁷ = 991638029 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 991638157.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991638107) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495819078 + 495819079.

It is an arithmetic number, because the mean of its divisors is an integer number (495819079).

Almost surely, 2^991638157 is an apocalyptic number.

It is an amenable number.

991638157 is a deficient number, since it is larger than the sum of its proper divisors (1).

991638157 is an equidigital number, since it uses as much as digits as its factorization.

991638157 is an evil number, because the sum of its binary digits is even.

The product of its digits is 408240, while the sum is 49.

The square root of 991638157 is about 31490.2867087615. The cubic root of 991638157 is about 997.2049137719.

The spelling of 991638157 in words is "nine hundred ninety-one million, six hundred thirty-eight thousand, one hundred fifty-seven".