721608781 has 2 divisors, whose sum is σ = 721608782. Its totient is φ = 721608780.

The previous prime is 721608779. The next prime is 721608787. The reversal of 721608781 is 187806127.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 550653156 + 170955625 = 23466^2 + 13075^2 .

It is a cyclic number.

It is not a de Polignac number, because 721608781 - 2¹ = 721608779 is a prime.

It is a super-2 number, since 2×721608781² = 1041438465632611922, which contains 22 as substring.

Together with 721608779, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721608787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360804390 + 360804391.

It is an arithmetic number, because the mean of its divisors is an integer number (360804391).

Almost surely, 2^721608781 is an apocalyptic number.

It is an amenable number.

721608781 is a deficient number, since it is larger than the sum of its proper divisors (1).

721608781 is an equidigital number, since it uses as much as digits as its factorization.

721608781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 37632, while the sum is 40.

The square root of 721608781 is about 26862.7768668840. The cubic root of 721608781 is about 896.9480081737.

The spelling of 721608781 in words is "seven hundred twenty-one million, six hundred eight thousand, seven hundred eighty-one".