31691521 has 2 divisors, whose sum is σ = 31691522. Its totient is φ = 31691520.

The previous prime is 31691507. The next prime is 31691531. The reversal of 31691521 is 12519613.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 26378496 + 5313025 = 5136^2 + 2305^2 .

It is a cyclic number.

It is not a de Polignac number, because 31691521 - 2¹³ = 31683329 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 31691521.

It is not a weakly prime, because it can be changed into another prime (31691501) 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, 15845760 + 15845761.

It is an arithmetic number, because the mean of its divisors is an integer number (15845761).

Almost surely, 2^31691521 is an apocalyptic number.

It is an amenable number.

31691521 is a deficient number, since it is larger than the sum of its proper divisors (1).

31691521 is an equidigital number, since it uses as much as digits as its factorization.

31691521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1620, while the sum is 28.

The square root of 31691521 is about 5629.5222710280. The cubic root of 31691521 is about 316.4567481641.

The spelling of 31691521 in words is "thirty-one million, six hundred ninety-one thousand, five hundred twenty-one".