31920021 has 48 divisors (see below), whose sum is σ = 57456000. Its totient is φ = 17430336.

The previous prime is 31920013. The next prime is 31920043. The reversal of 31920021 is 12002913.

It is a happy number.

It is not a de Polignac number, because 31920021 - 2³ = 31920013 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 31919976 and 31920003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31920071) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 29905 + ... + 30953.

It is an arithmetic number, because the mean of its divisors is an integer number (1197000).

Almost surely, 2^31920021 is an apocalyptic number.

It is an amenable number.

31920021 is a deficient number, since it is larger than the sum of its proper divisors (25535979).

31920021 is a wasteful number, since it uses less digits than its factorization.

31920021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1095 (or 1082 counting only the distinct ones).

The product of its (nonzero) digits is 108, while the sum is 18.

The square root of 31920021 is about 5649.7806152098. The cubic root of 31920021 is about 317.2154923373.

Adding to 31920021 its reverse (12002913), we get a palindrome (43922934).

The spelling of 31920021 in words is "thirty-one million, nine hundred twenty thousand, twenty-one".