261918460561 has 2 divisors, whose sum is σ = 261918460562. Its totient is φ = 261918460560.

The previous prime is 261918460553. The next prime is 261918460567. The reversal of 261918460561 is 165064819162.

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., 172843073536 + 89075387025 = 415744^2 + 298455^2 .

It is a cyclic number.

It is not a de Polignac number, because 261918460561 - 2³ = 261918460553 is a prime.

It is a super-2 number, since 2×261918460561² (a number of 24 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (261918460567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130959230280 + 130959230281.

It is an arithmetic number, because the mean of its divisors is an integer number (130959230281).

Almost surely, 2^261918460561 is an apocalyptic number.

It is an amenable number.

261918460561 is a deficient number, since it is larger than the sum of its proper divisors (1).

261918460561 is an equidigital number, since it uses as much as digits as its factorization.

261918460561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 622080, while the sum is 49.

The spelling of 261918460561 in words is "two hundred sixty-one billion, nine hundred eighteen million, four hundred sixty thousand, five hundred sixty-one".