31221221 has 4 divisors (see below), whose sum is σ = 31530444. Its totient is φ = 30912000.

The previous prime is 31221193. The next prime is 31221227. The reversal of 31221221 is 12212213.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 16120225 + 15100996 = 4015^2 + 3886^2 .

It is a cyclic number.

It is not a de Polignac number, because 31221221 - 2²² = 27026917 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 31221196 and 31221205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31221227) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 154460 + ... + 154661.

It is an arithmetic number, because the mean of its divisors is an integer number (7882611).

Almost surely, 2^31221221 is an apocalyptic number.

It is an amenable number.

31221221 is a deficient number, since it is larger than the sum of its proper divisors (309223).

31221221 is a wasteful number, since it uses less digits than its factorization.

31221221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 309222.

The product of its digits is 48, while the sum is 14.

The square root of 31221221 is about 5587.5952788297. The cubic root of 31221221 is about 314.8835413955.

Adding to 31221221 its reverse (12212213), we get a palindrome (43433434).

It can be divided in two parts, 3 and 1221221, that multiplied together give a palindrome (3663663).

The spelling of 31221221 in words is "thirty-one million, two hundred twenty-one thousand, two hundred twenty-one".