261138928681 has 2 divisors, whose sum is σ = 261138928682. Its totient is φ = 261138928680.

The previous prime is 261138928669. The next prime is 261138928691. The reversal of 261138928681 is 186829831162.

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., 198029450025 + 63109478656 = 445005^2 + 251216^2 .

It is a cyclic number.

It is not a de Polignac number, because 261138928681 - 2²⁹ = 260602057769 is a prime.

It is a super-2 number, since 2×261138928681² (a number of 24 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (261138928651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130569464340 + 130569464341.

It is an arithmetic number, because the mean of its divisors is an integer number (130569464341).

Almost surely, 2^261138928681 is an apocalyptic number.

It is an amenable number.

261138928681 is a deficient number, since it is larger than the sum of its proper divisors (1).

261138928681 is an equidigital number, since it uses as much as digits as its factorization.

261138928681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1990656, while the sum is 55.

The spelling of 261138928681 in words is "two hundred sixty-one billion, one hundred thirty-eight million, nine hundred twenty-eight thousand, six hundred eighty-one".