31213221 has 16 divisors (see below), whose sum is σ = 44924544. Its totient is φ = 19162944.

The previous prime is 31213213. The next prime is 31213243. The reversal of 31213221 is 12231213.

It is not a de Polignac number, because 31213221 - 2³ = 31213213 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 31213221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31213201) 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 in 15 ways as a sum of consecutive naturals, for example, 24615 + ... + 25851.

It is an arithmetic number, because the mean of its divisors is an integer number (2807784).

Almost surely, 2^31213221 is an apocalyptic number.

It is an amenable number.

31213221 is a deficient number, since it is larger than the sum of its proper divisors (13711323).

31213221 is a wasteful number, since it uses less digits than its factorization.

31213221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1900.

The product of its digits is 72, while the sum is 15.

The square root of 31213221 is about 5586.8793615041. The cubic root of 31213221 is about 314.8566442677.

Adding to 31213221 its reverse (12231213), we get a palindrome (43444434).

The spelling of 31213221 in words is "thirty-one million, two hundred thirteen thousand, two hundred twenty-one".