231220721 has 2 divisors, whose sum is σ = 231220722. Its totient is φ = 231220720.

The previous prime is 231220697. The next prime is 231220727. The reversal of 231220721 is 127022132.

231220721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 128482225 + 102738496 = 11335^2 + 10136^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-231220721 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 231220693 and 231220702.

It is not a weakly prime, because it can be changed into another prime (231220727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 115610360 + 115610361.

It is an arithmetic number, because the mean of its divisors is an integer number (115610361).

Almost surely, 2^231220721 is an apocalyptic number.

It is an amenable number.

231220721 is a deficient number, since it is larger than the sum of its proper divisors (1).

231220721 is an equidigital number, since it uses as much as digits as its factorization.

231220721 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 231220721 is about 15205.9436076818. The cubic root of 231220721 is about 613.7746071880.

Adding to 231220721 its reverse (127022132), we get a palindrome (358242853).

The spelling of 231220721 in words is "two hundred thirty-one million, two hundred twenty thousand, seven hundred twenty-one".