31320721 has 12 divisors (see below), whose sum is σ = 33700212. Its totient is φ = 29094624.

The previous prime is 31320713. The next prime is 31320739. The reversal of 31320721 is 12702313.

It can be written as a sum of positive squares in 2 ways, for example, as 9828225 + 21492496 = 3135^2 + 4636^2 .

It is not a de Polignac number, because 31320721 - 2³ = 31320713 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (19).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (31320701) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 18315 + ... + 19951.

It is an arithmetic number, because the mean of its divisors is an integer number (2808351).

Almost surely, 2^31320721 is an apocalyptic number.

It is an amenable number.

31320721 is a deficient number, since it is larger than the sum of its proper divisors (2379491).

31320721 is a wasteful number, since it uses less digits than its factorization.

31320721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1728 (or 1709 counting only the distinct ones).

The product of its (nonzero) digits is 252, while the sum is 19.

The square root of 31320721 is about 5596.4918475774. The cubic root of 31320721 is about 315.2176911285.

It can be divided in two parts, 31320 and 721, that added together give a square (32041 = 179²).

The spelling of 31320721 in words is "thirty-one million, three hundred twenty thousand, seven hundred twenty-one".