261787842817 has 4 divisors (see below), whose sum is σ = 268172912196. Its totient is φ = 255402773440.

The previous prime is 261787842803. The next prime is 261787842851. The reversal of 261787842817 is 718248787162.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3240000241 + 258547842576 = 56921^2 + 508476^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261787842817 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261787842857) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3192534628 + ... + 3192534709.

It is an arithmetic number, because the mean of its divisors is an integer number (67043228049).

Almost surely, 2^261787842817 is an apocalyptic number.

It is an amenable number.

261787842817 is a deficient number, since it is larger than the sum of its proper divisors (6385069379).

261787842817 is an equidigital number, since it uses as much as digits as its factorization.

261787842817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6385069378.

The product of its digits is 16859136, while the sum is 61.

The spelling of 261787842817 in words is "two hundred sixty-one billion, seven hundred eighty-seven million, eight hundred forty-two thousand, eight hundred seventeen".