31221 has 6 divisors (see below), whose sum is σ = 45110. Its totient is φ = 20808.

The previous prime is 31219. The next prime is 31223. The reversal of 31221 is 12213.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (31219) and next prime (31223).

It can be written as a sum of positive squares in only one way, i.e., 18225 + 12996 = 135^2 + 114^2 .

It is not a de Polignac number, because 31221 - 2¹ = 31219 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9), and also a Moran number because the ratio is a prime number: 3469 = 31221 / (3 + 1 + 2 + 2 + 1).

It is a Duffinian number.

31221 is a lucky number.

It is a nialpdrome in base 14.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 31221.

It is not an unprimeable number, because it can be changed into a prime (31223) 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 5 ways as a sum of consecutive naturals, for example, 1726 + ... + 1743.

2³¹²²¹ is an apocalyptic number.

It is an amenable number.

31221 is a deficient number, since it is larger than the sum of its proper divisors (13889).

31221 is a wasteful number, since it uses less digits than its factorization.

31221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3475 (or 3472 counting only the distinct ones).

The product of its digits is 12, while the sum is 9.

The square root of 31221 is about 176.6946518715. The cubic root of 31221 is about 31.4882798424.

Adding to 31221 its reverse (12213), we get a palindrome (43434).

It can be divided in two parts, 312 and 21, that added together give a palindrome (333).

The spelling of 31221 in words is "thirty-one thousand, two hundred twenty-one".