261543742517565 has 48 divisors (see below), whose sum is σ = 496561750542000. Its totient is φ = 126757643421696.

The previous prime is 261543742517513. The next prime is 261543742517581. The reversal of 261543742517565 is 565715247345162.

261543742517565 is a `hidden beast` number, since 2 + 6 + 1 + 5 + 4 + 37 + 4 + 25 + 17 + 565 = 666.

It can be written as a sum of positive squares in 8 ways, for example, as 2618891653401 + 258924850864164 = 1618299^2 + 16091142^2 .

It is not a de Polignac number, because 261543742517565 - 2¹⁶ = 261543742452029 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 5894585490 + ... + 5894629859.

It is an arithmetic number, because the mean of its divisors is an integer number (10345036469625).

Almost surely, 2^{261543742517565} is an apocalyptic number.

It is an amenable number.

261543742517565 is a deficient number, since it is larger than the sum of its proper divisors (235018008024435).

261543742517565 is a wasteful number, since it uses less digits than its factorization.

261543742517565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11789215406 (or 11789215403 counting only the distinct ones).

The product of its digits is 211680000, while the sum is 63.

The spelling of 261543742517565 in words is "two hundred sixty-one trillion, five hundred forty-three billion, seven hundred forty-two million, five hundred seventeen thousand, five hundred sixty-five".