721665056670121 has 2 divisors, whose sum is σ = 721665056670122. Its totient is φ = 721665056670120.

The previous prime is 721665056670029. The next prime is 721665056670133. The reversal of 721665056670121 is 121076650566127.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 645867329766400 + 75797726903721 = 25413920^2 + 8706189^2 .

It is an emirp because it is prime and its reverse (121076650566127) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 721665056670121 - 2¹⁹ = 721665056145833 is a prime.

It is a super-2 number, since 2×721665056670121² (a number of 31 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (721665056670221) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360832528335060 + 360832528335061.

It is an arithmetic number, because the mean of its divisors is an integer number (360832528335061).

Almost surely, 2^{721665056670121} is an apocalyptic number.

It is an amenable number.

721665056670121 is a deficient number, since it is larger than the sum of its proper divisors (1).

721665056670121 is an equidigital number, since it uses as much as digits as its factorization.

721665056670121 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6350400, while the sum is 55.

The spelling of 721665056670121 in words is "seven hundred twenty-one trillion, six hundred sixty-five billion, fifty-six million, six hundred seventy thousand, one hundred twenty-one".