261631865557 has 2 divisors, whose sum is σ = 261631865558. Its totient is φ = 261631865556.

The previous prime is 261631865501. The next prime is 261631865783. The reversal of 261631865557 is 755568136162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 215476069636 + 46155795921 = 464194^2 + 214839^2 .

It is a cyclic number.

It is not a de Polignac number, because 261631865557 - 2³⁵ = 227272127189 is a prime.

It is a super-2 number, since 2×261631865557² (a number of 24 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 261631865498 and 261631865507.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261631865057) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130815932778 + 130815932779.

It is an arithmetic number, because the mean of its divisors is an integer number (130815932779).

Almost surely, 2^261631865557 is an apocalyptic number.

It is an amenable number.

261631865557 is a deficient number, since it is larger than the sum of its proper divisors (1).

261631865557 is an equidigital number, since it uses as much as digits as its factorization.

261631865557 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9072000, while the sum is 55.

The spelling of 261631865557 in words is "two hundred sixty-one billion, six hundred thirty-one million, eight hundred sixty-five thousand, five hundred fifty-seven".