721306661 has 2 divisors, whose sum is σ = 721306662. Its totient is φ = 721306660.

The previous prime is 721306643. The next prime is 721306669. The reversal of 721306661 is 166603127.

721306661 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., 680218561 + 41088100 = 26081^2 + 6410^2 .

It is an emirp because it is prime and its reverse (166603127) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-721306661 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721306669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360653330 + 360653331.

It is an arithmetic number, because the mean of its divisors is an integer number (360653331).

Almost surely, 2^721306661 is an apocalyptic number.

It is an amenable number.

721306661 is a deficient number, since it is larger than the sum of its proper divisors (1).

721306661 is an equidigital number, since it uses as much as digits as its factorization.

721306661 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 9072, while the sum is 32.

The square root of 721306661 is about 26857.1528833568. The cubic root of 721306661 is about 896.8228139473.

Adding to 721306661 its reverse (166603127), we get a palindrome (887909788).

It can be divided in two parts, 7213066 and 61, that added together give a palindrome (7213127).

The spelling of 721306661 in words is "seven hundred twenty-one million, three hundred six thousand, six hundred sixty-one".