31891621 has 2 divisors, whose sum is σ = 31891622. Its totient is φ = 31891620.

The previous prime is 31891603. The next prime is 31891631. The reversal of 31891621 is 12619813.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20802721 + 11088900 = 4561^2 + 3330^2 .

It is an emirp because it is prime and its reverse (12619813) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 31891621 - 2⁹ = 31891109 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31891631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15945810 + 15945811.

It is an arithmetic number, because the mean of its divisors is an integer number (15945811).

Almost surely, 2^31891621 is an apocalyptic number.

It is an amenable number.

31891621 is a deficient number, since it is larger than the sum of its proper divisors (1).

31891621 is an equidigital number, since it uses as much as digits as its factorization.

31891621 is an evil number, because the sum of its binary digits is even.

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

The square root of 31891621 is about 5647.2666839808. The cubic root of 31891621 is about 317.1213863725.

The spelling of 31891621 in words is "thirty-one million, eight hundred ninety-one thousand, six hundred twenty-one".