1266820865 has 4 divisors (see below), whose sum is σ = 1520185044. Its totient is φ = 1013456688.

The previous prime is 1266820847. The next prime is 1266820871. The reversal of 1266820865 is 5680286621.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 5680286621 = 149 ⋅38122729.

It can be written as a sum of positive squares in 2 ways, for example, as 904565776 + 362255089 = 30076^2 + 19033^2 .

It is a cyclic number.

It is not a de Polignac number, because 1266820865 - 2²⁰ = 1265772289 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 126682082 + ... + 126682091.

It is an arithmetic number, because the mean of its divisors is an integer number (380046261).

Almost surely, 2^1266820865 is an apocalyptic number.

It is an amenable number.

1266820865 is a deficient number, since it is larger than the sum of its proper divisors (253364179).

1266820865 is an equidigital number, since it uses as much as digits as its factorization.

1266820865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 253364178.

The product of its (nonzero) digits is 276480, while the sum is 44.

The square root of 1266820865 is about 35592.4270737470. The cubic root of 1266820865 is about 1082.0277590331.

It can be divided in two parts, 12668 and 20865, that added together give a palindrome (33533).

The spelling of 1266820865 in words is "one billion, two hundred sixty-six million, eight hundred twenty thousand, eight hundred sixty-five".