261138758561 has 2 divisors, whose sum is σ = 261138758562. Its totient is φ = 261138758560.

The previous prime is 261138758557. The next prime is 261138758611. The reversal of 261138758561 is 165857831162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 181420624225 + 79718134336 = 425935^2 + 282344^2 .

It is a cyclic number.

It is not a de Polignac number, because 261138758561 - 2² = 261138758557 is a prime.

It is not a weakly prime, because it can be changed into another prime (261138758501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130569379280 + 130569379281.

It is an arithmetic number, because the mean of its divisors is an integer number (130569379281).

Almost surely, 2^261138758561 is an apocalyptic number.

It is an amenable number.

261138758561 is a deficient number, since it is larger than the sum of its proper divisors (1).

261138758561 is an equidigital number, since it uses as much as digits as its factorization.

261138758561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2419200, while the sum is 53.

The spelling of 261138758561 in words is "two hundred sixty-one billion, one hundred thirty-eight million, seven hundred fifty-eight thousand, five hundred sixty-one".