331987991 has 2 divisors, whose sum is σ = 331987992. Its totient is φ = 331987990.

The previous prime is 331987979. The next prime is 331988009. The reversal of 331987991 is 199789133.

It is a happy number.

It is a weak prime.

It is an emirp because it is prime and its reverse (199789133) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 331987991 - 2¹⁸ = 331725847 is a prime.

It is a super-2 number, since 2×331987991² = 220432052336432162, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (331987921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 165993995 + 165993996.

It is an arithmetic number, because the mean of its divisors is an integer number (165993996).

Almost surely, 2^331987991 is an apocalyptic number.

331987991 is a deficient number, since it is larger than the sum of its proper divisors (1).

331987991 is an equidigital number, since it uses as much as digits as its factorization.

331987991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 367416, while the sum is 50.

The square root of 331987991 is about 18220.5376155590. The cubic root of 331987991 is about 692.4272083080.

The spelling of 331987991 in words is "three hundred thirty-one million, nine hundred eighty-seven thousand, nine hundred ninety-one".