31720221 has 16 divisors (see below), whose sum is σ = 50608320. Its totient is φ = 19519920.

The previous prime is 31720219. The next prime is 31720237. The reversal of 31720221 is 12202713.

It is not a de Polignac number, because 31720221 - 2¹ = 31720219 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 31720194 and 31720203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31720121) 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 15 ways as a sum of consecutive naturals, for example, 44835 + ... + 45536.

It is an arithmetic number, because the mean of its divisors is an integer number (3163020).

Almost surely, 2^31720221 is an apocalyptic number.

It is an amenable number.

31720221 is a deficient number, since it is larger than the sum of its proper divisors (18888099).

31720221 is a wasteful number, since it uses less digits than its factorization.

31720221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90393 (or 90387 counting only the distinct ones).

The product of its (nonzero) digits is 168, while the sum is 18.

The square root of 31720221 is about 5632.0707559476. The cubic root of 31720221 is about 316.5522476132.

Adding to 31720221 its reverse (12202713), we get a palindrome (43922934).

The spelling of 31720221 in words is "thirty-one million, seven hundred twenty thousand, two hundred twenty-one".