12721815721 has 2 divisors, whose sum is σ = 12721815722. Its totient is φ = 12721815720.

The previous prime is 12721815703. The next prime is 12721815737. The reversal of 12721815721 is 12751812721.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 8478726400 + 4243089321 = 92080^2 + 65139^2 .

It is a cyclic number.

It is not a de Polignac number, because 12721815721 - 2¹¹ = 12721813673 is a prime.

It is not a weakly prime, because it can be changed into another prime (12721815781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 6360907860 + 6360907861.

It is an arithmetic number, because the mean of its divisors is an integer number (6360907861).

Almost surely, 2^12721815721 is an apocalyptic number.

It is an amenable number.

12721815721 is a deficient number, since it is larger than the sum of its proper divisors (1).

12721815721 is an equidigital number, since it uses as much as digits as its factorization.

12721815721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15680, while the sum is 37.

The spelling of 12721815721 in words is "twelve billion, seven hundred twenty-one million, eight hundred fifteen thousand, seven hundred twenty-one".