157991 has 2 divisors, whose sum is σ = 157992.
Its totient is φ = 157990.
The previous prime is 157951. The next prime is 157999. The reversal of 157991 is 199751.
157991 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 is an emirp because it is prime and its reverse (199751) is a distict prime.
It is a cyclic number.
It is not a de Polignac number, because 157991 - 210 = 156967 is a prime.
It is a super-2 number, since 2×1579912 = 49922312162, which contains 22 as substring.
It is a congruent number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 157991.
It is not a weakly prime, because it can be changed into another prime (157999) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 78995 + 78996.
It is an arithmetic number, because the mean of its divisors is an integer number (78996).
2157991 is an apocalyptic number.
157991 is a deficient number, since it is larger than the sum of its proper divisors (1).
157991 is an equidigital number, since it uses as much as digits as its factorization.
157991 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 2835, while the sum is 32.
The square root of 157991 is about 397.4808171472.
The cubic root of 157991 is about 54.0601752595.
The spelling of 157991 in words is "one hundred fifty-seven thousand, nine hundred ninety-one".