31521221 has 4 divisors (see below), whose sum is σ = 31598700. Its totient is φ = 31443744.

The previous prime is 31521157. The next prime is 31521223. The reversal of 31521221 is 12212513.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12212513 = 733 ⋅16661.

It can be written as a sum of positive squares in 2 ways, for example, as 29008996 + 2512225 = 5386^2 + 1585^2 .

It is a cyclic number.

It is not a de Polignac number, because 31521221 - 2⁶ = 31521157 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 31521221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31521223) 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, 38126 + ... + 38943.

It is an arithmetic number, because the mean of its divisors is an integer number (7899675).

Almost surely, 2^31521221 is an apocalyptic number.

It is an amenable number.

31521221 is a deficient number, since it is larger than the sum of its proper divisors (77479).

31521221 is an equidigital number, since it uses as much as digits as its factorization.

31521221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 77478.

The product of its digits is 120, while the sum is 17.

The square root of 31521221 is about 5614.3762788043. The cubic root of 31521221 is about 315.8888843158. Note that the first 5 decimals are identical.

Adding to 31521221 its reverse (12212513), we get a palindrome (43733734).

The spelling of 31521221 in words is "thirty-one million, five hundred twenty-one thousand, two hundred twenty-one".