721407307661 has 2 divisors, whose sum is σ = 721407307662. Its totient is φ = 721407307660.

The previous prime is 721407307651. The next prime is 721407307721. The reversal of 721407307661 is 166703704127.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 694732252036 + 26675055625 = 833506^2 + 163325^2 .

It is an emirp because it is prime and its reverse (166703704127) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-721407307661 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721407307651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360703653830 + 360703653831.

It is an arithmetic number, because the mean of its divisors is an integer number (360703653831).

Almost surely, 2^721407307661 is an apocalyptic number.

It is an amenable number.

721407307661 is a deficient number, since it is larger than the sum of its proper divisors (1).

721407307661 is an equidigital number, since it uses as much as digits as its factorization.

721407307661 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 296352, while the sum is 44.

The spelling of 721407307661 in words is "seven hundred twenty-one billion, four hundred seven million, three hundred seven thousand, six hundred sixty-one".