31621561 has 2 divisors, whose sum is σ = 31621562. Its totient is φ = 31621560.

The previous prime is 31621559. The next prime is 31621591. The reversal of 31621561 is 16512613.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 31573161 + 48400 = 5619^2 + 220^2 .

It is a cyclic number.

It is not a de Polignac number, because 31621561 - 2¹ = 31621559 is a prime.

Together with 31621559, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (31621501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15810780 + 15810781.

It is an arithmetic number, because the mean of its divisors is an integer number (15810781).

Almost surely, 2^31621561 is an apocalyptic number.

It is an amenable number.

31621561 is a deficient number, since it is larger than the sum of its proper divisors (1).

31621561 is an equidigital number, since it uses as much as digits as its factorization.

31621561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1080, while the sum is 25.

The square root of 31621561 is about 5623.3051668925. The cubic root of 31621561 is about 316.2237139593.

The spelling of 31621561 in words is "thirty-one million, six hundred twenty-one thousand, five hundred sixty-one".