31129991 has 2 divisors, whose sum is σ = 31129992. Its totient is φ = 31129990.

The previous prime is 31129981. The next prime is 31130039. The reversal of 31129991 is 19992113.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 31129991 - 2⁶ = 31129927 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 (31129981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15564995 + 15564996.

It is an arithmetic number, because the mean of its divisors is an integer number (15564996).

Almost surely, 2^31129991 is an apocalyptic number.

31129991 is a deficient number, since it is larger than the sum of its proper divisors (1).

31129991 is an equidigital number, since it uses as much as digits as its factorization.

31129991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4374, while the sum is 35.

The square root of 31129991 is about 5579.4256872908. The cubic root of 31129991 is about 314.5765402546.

The spelling of 31129991 in words is "thirty-one million, one hundred twenty-nine thousand, nine hundred ninety-one".