261543742517581 has 2 divisors, whose sum is σ = 261543742517582. Its totient is φ = 261543742517580.

The previous prime is 261543742517513. The next prime is 261543742517663. The reversal of 261543742517581 is 185715247345162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 240620747922025 + 20922994595556 = 15511955^2 + 4574166^2 .

It is a cyclic number.

It is not a de Polignac number, because 261543742517581 - 2¹¹ = 261543742515533 is a prime.

It is a super-2 number, since 2×261543742517581² (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 (261543742517381) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (31) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130771871258790 + 130771871258791.

It is an arithmetic number, because the mean of its divisors is an integer number (130771871258791).

Almost surely, 2^{261543742517581} is an apocalyptic number.

It is an amenable number.

261543742517581 is a deficient number, since it is larger than the sum of its proper divisors (1).

261543742517581 is an equidigital number, since it uses as much as digits as its factorization.

261543742517581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 56448000, while the sum is 61.

The spelling of 261543742517581 in words is "two hundred sixty-one trillion, five hundred forty-three billion, seven hundred forty-two million, five hundred seventeen thousand, five hundred eighty-one".