31666721 has 2 divisors, whose sum is σ = 31666722. Its totient is φ = 31666720.

The previous prime is 31666703. The next prime is 31666751. The reversal of 31666721 is 12766613.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 30129121 + 1537600 = 5489^2 + 1240^2 .

It is a cyclic number.

It is not a de Polignac number, because 31666721 - 2¹⁴ = 31650337 is a prime.

It is a Chen prime.

It is equal to p_1954481 and since 31666721 and 1954481 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (31666751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15833360 + 15833361.

It is an arithmetic number, because the mean of its divisors is an integer number (15833361).

Almost surely, 2^31666721 is an apocalyptic number.

It is an amenable number.

31666721 is a deficient number, since it is larger than the sum of its proper divisors (1).

31666721 is an equidigital number, since it uses as much as digits as its factorization.

31666721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9072, while the sum is 32.

The square root of 31666721 is about 5627.3191663527. The cubic root of 31666721 is about 316.3741795446.

The spelling of 31666721 in words is "thirty-one million, six hundred sixty-six thousand, seven hundred twenty-one".