31663561 has 2 divisors, whose sum is σ = 31663562. Its totient is φ = 31663560.

The previous prime is 31663559. The next prime is 31663573. The reversal of 31663561 is 16536613.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 26574025 + 5089536 = 5155^2 + 2256^2 .

It is an emirp because it is prime and its reverse (16536613) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 31663561 - 2¹ = 31663559 is a prime.

Together with 31663559, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (31663591) 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, 15831780 + 15831781.

It is an arithmetic number, because the mean of its divisors is an integer number (15831781).

Almost surely, 2^31663561 is an apocalyptic number.

It is an amenable number.

31663561 is a deficient number, since it is larger than the sum of its proper divisors (1).

31663561 is an equidigital number, since it uses as much as digits as its factorization.

31663561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9720, while the sum is 31.

The square root of 31663561 is about 5627.0383862206. The cubic root of 31663561 is about 316.3636556083.

It can be divided in two parts, 3166 and 3561, that multiplied together give a triangular number (11274126 = T₄₇₄₈).

The spelling of 31663561 in words is "thirty-one million, six hundred sixty-three thousand, five hundred sixty-one".