265561721 has 2 divisors, whose sum is σ = 265561722. Its totient is φ = 265561720.

The previous prime is 265561711. The next prime is 265561741. The reversal of 265561721 is 127165562.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 259854400 + 5707321 = 16120^2 + 2389^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-265561721 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (265561711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 132780860 + 132780861.

It is an arithmetic number, because the mean of its divisors is an integer number (132780861).

Almost surely, 2^265561721 is an apocalyptic number.

It is an amenable number.

265561721 is a deficient number, since it is larger than the sum of its proper divisors (1).

265561721 is an equidigital number, since it uses as much as digits as its factorization.

265561721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 25200, while the sum is 35.

The square root of 265561721 is about 16296.0645862736. The cubic root of 265561721 is about 642.7693479234.

The spelling of 265561721 in words is "two hundred sixty-five million, five hundred sixty-one thousand, seven hundred twenty-one".