318181991 has 2 divisors, whose sum is σ = 318181992. Its totient is φ = 318181990.

The previous prime is 318181973. The next prime is 318182087. The reversal of 318181991 is 199181813.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 318181991 - 2²⁶ = 251073127 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (318181951) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 159090995 + 159090996.

It is an arithmetic number, because the mean of its divisors is an integer number (159090996).

Almost surely, 2^318181991 is an apocalyptic number.

318181991 is a deficient number, since it is larger than the sum of its proper divisors (1).

318181991 is an equidigital number, since it uses as much as digits as its factorization.

318181991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15552, while the sum is 41.

The square root of 318181991 is about 17837.6565445128. The cubic root of 318181991 is about 682.6926046954.

The spelling of 318181991 in words is "three hundred eighteen million, one hundred eighty-one thousand, nine hundred ninety-one".