31689221 has 4 divisors (see below), whose sum is σ = 32016012. Its totient is φ = 31362432.

The previous prime is 31689157. The next prime is 31689247. The reversal of 31689221 is 12298613.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12298613 = 863 ⋅14251.

It can be written as a sum of positive squares in 2 ways, for example, as 16564900 + 15124321 = 4070^2 + 3889^2 .

It is a cyclic number.

It is not a de Polignac number, because 31689221 - 2⁶ = 31689157 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31689521) 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 in 3 ways as a sum of consecutive naturals, for example, 163250 + ... + 163443.

It is an arithmetic number, because the mean of its divisors is an integer number (8004003).

Almost surely, 2^31689221 is an apocalyptic number.

It is an amenable number.

31689221 is a deficient number, since it is larger than the sum of its proper divisors (326791).

31689221 is an equidigital number, since it uses as much as digits as its factorization.

31689221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 326790.

The product of its digits is 5184, while the sum is 32.

The square root of 31689221 is about 5629.3179871100. The cubic root of 31689221 is about 316.4490924031.

The spelling of 31689221 in words is "thirty-one million, six hundred eighty-nine thousand, two hundred twenty-one".