2561561344721 has 2 divisors, whose sum is σ = 2561561344722. Its totient is φ = 2561561344720.

The previous prime is 2561561344703. The next prime is 2561561344781. The reversal of 2561561344721 is 1274431651652.

2561561344721 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 2358340704721 + 203220640000 = 1535689^2 + 450800^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2561561344721 is a prime.

It is not a weakly prime, because it can be changed into another prime (2561561344781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1280780672360 + 1280780672361.

It is an arithmetic number, because the mean of its divisors is an integer number (1280780672361).

Almost surely, 2^{2561561344721} is an apocalyptic number.

It is an amenable number.

2561561344721 is a deficient number, since it is larger than the sum of its proper divisors (1).

2561561344721 is an equidigital number, since it uses as much as digits as its factorization.

2561561344721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1209600, while the sum is 47.

The spelling of 2561561344721 in words is "two trillion, five hundred sixty-one billion, five hundred sixty-one million, three hundred forty-four thousand, seven hundred twenty-one".