1266236561 has 2 divisors, whose sum is σ = 1266236562. Its totient is φ = 1266236560.

The previous prime is 1266236519. The next prime is 1266236563. The reversal of 1266236561 is 1656326621.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1181228161 + 85008400 = 34369^2 + 9220^2 .

It is a cyclic number.

It is not a de Polignac number, because 1266236561 - 2¹⁸ = 1265974417 is a prime.

It is a Sophie Germain prime.

Together with 1266236563, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (1266236563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 633118280 + 633118281.

It is an arithmetic number, because the mean of its divisors is an integer number (633118281).

Almost surely, 2^1266236561 is an apocalyptic number.

It is an amenable number.

1266236561 is a deficient number, since it is larger than the sum of its proper divisors (1).

1266236561 is an equidigital number, since it uses as much as digits as its factorization.

1266236561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 77760, while the sum is 38.

The square root of 1266236561 is about 35584.2178641037. The cubic root of 1266236561 is about 1081.8613765573.

The spelling of 1266236561 in words is "one billion, two hundred sixty-six million, two hundred thirty-six thousand, five hundred sixty-one".