87991 has 2 divisors, whose sum is σ = 87992.
Its totient is φ = 87990.
The previous prime is 87977. The next prime is 88001. The reversal of 87991 is 19978.
It is a strong prime.
It is a cyclic number.
It is not a de Polignac number, because 87991 - 25 = 87959 is a prime.
It is a pancake number, because a pancake can be divided into 87991 parts by 419 straight cuts.
87991 is a lucky number.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (87911) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 43995 + 43996.
It is an arithmetic number, because the mean of its divisors is an integer number (43996).
287991 is an apocalyptic number.
87991 is a deficient number, since it is larger than the sum of its proper divisors (1).
87991 is an equidigital number, since it uses as much as digits as its factorization.
87991 is an evil number, because the sum of its binary digits is even.
The product of its digits is 4536, while the sum is 34.
The square root of 87991 is about 296.6327695990.
The cubic root of 87991 is about 44.4780854096.
The spelling of 87991 in words is "eighty-seven thousand, nine hundred ninety-one".