721317661 has 2 divisors, whose sum is σ = 721317662. Its totient is φ = 721317660.

The previous prime is 721317631. The next prime is 721317679. The reversal of 721317661 is 166713127.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 365995161 + 355322500 = 19131^2 + 18850^2 .

It is a cyclic number.

It is not a de Polignac number, because 721317661 - 2⁵ = 721317629 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721317631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360658830 + 360658831.

It is an arithmetic number, because the mean of its divisors is an integer number (360658831).

Almost surely, 2^721317661 is an apocalyptic number.

It is an amenable number.

721317661 is a deficient number, since it is larger than the sum of its proper divisors (1).

721317661 is an equidigital number, since it uses as much as digits as its factorization.

721317661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10584, while the sum is 34.

The square root of 721317661 is about 26857.3576697336. The cubic root of 721317661 is about 896.8273728038.

The spelling of 721317661 in words is "seven hundred twenty-one million, three hundred seventeen thousand, six hundred sixty-one".