31240721 has 2 divisors, whose sum is σ = 31240722. Its totient is φ = 31240720.

The previous prime is 31240711. The next prime is 31240733. The reversal of 31240721 is 12704213.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 24010000 + 7230721 = 4900^2 + 2689^2 .

It is an emirp because it is prime and its reverse (12704213) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 31240721 - 2¹⁰ = 31239697 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 31240693 and 31240702.

It is not a weakly prime, because it can be changed into another prime (31240711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15620360 + 15620361.

It is an arithmetic number, because the mean of its divisors is an integer number (15620361).

Almost surely, 2^31240721 is an apocalyptic number.

It is an amenable number.

31240721 is a deficient number, since it is larger than the sum of its proper divisors (1).

31240721 is an equidigital number, since it uses as much as digits as its factorization.

31240721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 336, while the sum is 20.

The square root of 31240721 is about 5589.3399431418. The cubic root of 31240721 is about 314.9490839011.

Adding to 31240721 its reverse (12704213), we get a palindrome (43944934).

The spelling of 31240721 in words is "thirty-one million, two hundred forty thousand, seven hundred twenty-one".