721608821 has 2 divisors, whose sum is σ = 721608822. Its totient is φ = 721608820.

The previous prime is 721608787. The next prime is 721608829. The reversal of 721608821 is 128806127.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 720331921 + 1276900 = 26839^2 + 1130^2 .

It is a cyclic number.

It is not a de Polignac number, because 721608821 - 2¹⁴ = 721592437 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721608829) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360804410 + 360804411.

It is an arithmetic number, because the mean of its divisors is an integer number (360804411).

Almost surely, 2^721608821 is an apocalyptic number.

It is an amenable number.

721608821 is a deficient number, since it is larger than the sum of its proper divisors (1).

721608821 is an equidigital number, since it uses as much as digits as its factorization.

721608821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10752, while the sum is 35.

The square root of 721608821 is about 26862.7776114087. Note that the first 3 decimals coincide. The cubic root of 721608821 is about 896.9480247468.

The spelling of 721608821 in words is "seven hundred twenty-one million, six hundred eight thousand, eight hundred twenty-one".