31991621 has 2 divisors, whose sum is σ = 31991622. Its totient is φ = 31991620.

The previous prime is 31991591. The next prime is 31991639. The reversal of 31991621 is 12619913.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 29920900 + 2070721 = 5470^2 + 1439^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-31991621 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 (31991221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15995810 + 15995811.

It is an arithmetic number, because the mean of its divisors is an integer number (15995811).

Almost surely, 2^31991621 is an apocalyptic number.

It is an amenable number.

31991621 is a deficient number, since it is larger than the sum of its proper divisors (1).

31991621 is an equidigital number, since it uses as much as digits as its factorization.

31991621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2916, while the sum is 32.

The square root of 31991621 is about 5656.1135950403. The cubic root of 31991621 is about 317.4524979051.

The spelling of 31991621 in words is "thirty-one million, nine hundred ninety-one thousand, six hundred twenty-one".