261431265021781 has 2 divisors, whose sum is σ = 261431265021782. Its totient is φ = 261431265021780.

The previous prime is 261431265021769. The next prime is 261431265021889. The reversal of 261431265021781 is 187120562134162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 207555165900625 + 53876099121156 = 14406775^2 + 7340034^2 .

It is a cyclic number.

It is not a de Polignac number, because 261431265021781 - 2⁷ = 261431265021653 is a prime.

It is a super-2 number, since 2×261431265021781² (a number of 30 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261431265121781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (29) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130715632510890 + 130715632510891.

It is an arithmetic number, because the mean of its divisors is an integer number (130715632510891).

Almost surely, 2^{261431265021781} is an apocalyptic number.

It is an amenable number.

261431265021781 is a deficient number, since it is larger than the sum of its proper divisors (1).

261431265021781 is an equidigital number, since it uses as much as digits as its factorization.

261431265021781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 967680, while the sum is 49.

The spelling of 261431265021781 in words is "two hundred sixty-one trillion, four hundred thirty-one billion, two hundred sixty-five million, twenty-one thousand, seven hundred eighty-one".