31201991 has 2 divisors, whose sum is σ = 31201992. Its totient is φ = 31201990.

The previous prime is 31201981. The next prime is 31202051. The reversal of 31201991 is 19910213.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-31201991 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 31201991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31201901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15600995 + 15600996.

It is an arithmetic number, because the mean of its divisors is an integer number (15600996).

Almost surely, 2^31201991 is an apocalyptic number.

31201991 is a deficient number, since it is larger than the sum of its proper divisors (1).

31201991 is an equidigital number, since it uses as much as digits as its factorization.

31201991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 486, while the sum is 26.

The square root of 31201991 is about 5585.8742377537. The cubic root of 31201991 is about 314.8188796695.

The spelling of 31201991 in words is "thirty-one million, two hundred one thousand, nine hundred ninety-one".