37991 has 2 divisors, whose sum is σ = 37992. Its totient is φ = 37990.

The previous prime is 37987. The next prime is 37993. The reversal of 37991 is 19973.

37991 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 (19973) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 37991 - 2² = 37987 is a prime.

It is a Sophie Germain prime.

Together with 37993, it forms a pair of twin primes.

It is a Chen prime.

It is a nialpdrome in base 14.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (37993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 18995 + 18996.

It is an arithmetic number, because the mean of its divisors is an integer number (18996).

2³⁷⁹⁹¹ is an apocalyptic number.

37991 is a deficient number, since it is larger than the sum of its proper divisors (1).

37991 is an equidigital number, since it uses as much as digits as its factorization.

37991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1701, while the sum is 29.

The square root of 37991 is about 194.9128010162. The cubic root of 37991 is about 33.6170996673.

The spelling of 37991 in words is "thirty-seven thousand, nine hundred ninety-one".