261556872665 has 16 divisors (see below), whose sum is σ = 347224288896. Its totient is φ = 187543977600.

The previous prime is 261556872659. The next prime is 261556872671. The reversal of 261556872665 is 566278655162.

It is an interprime number because it is at equal distance from previous prime (261556872659) and next prime (261556872671).

It is a de Polignac number, because none of the positive numbers 2^k-261556872665 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 33486092 + ... + 33493901.

It is an arithmetic number, because the mean of its divisors is an integer number (21701518056).

Almost surely, 2^261556872665 is an apocalyptic number.

It is an amenable number.

261556872665 is a deficient number, since it is larger than the sum of its proper divisors (85667416231).

261556872665 is a wasteful number, since it uses less digits than its factorization.

261556872665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66980080.

The product of its digits is 36288000, while the sum is 59.

The spelling of 261556872665 in words is "two hundred sixty-one billion, five hundred fifty-six million, eight hundred seventy-two thousand, six hundred sixty-five".