31621981 has 2 divisors, whose sum is σ = 31621982. Its totient is φ = 31621980.

The previous prime is 31621979. The next prime is 31622047. The reversal of 31621981 is 18912613.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 22410756 + 9211225 = 4734^2 + 3035^2 .

It is a cyclic number.

It is not a de Polignac number, because 31621981 - 2¹ = 31621979 is a prime.

It is a super-2 number, since 2×31621981² = 1999899364728722, which contains 22 as substring.

Together with 31621979, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31621901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15810990 + 15810991.

It is an arithmetic number, because the mean of its divisors is an integer number (15810991).

Almost surely, 2^31621981 is an apocalyptic number.

It is an amenable number.

31621981 is a deficient number, since it is larger than the sum of its proper divisors (1).

31621981 is an equidigital number, since it uses as much as digits as its factorization.

31621981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2592, while the sum is 31.

The square root of 31621981 is about 5623.3425113539. The cubic root of 31621981 is about 316.2251139890.

The spelling of 31621981 in words is "thirty-one million, six hundred twenty-one thousand, nine hundred eighty-one".