1261217809 has 2 divisors, whose sum is σ = 1261217810. Its totient is φ = 1261217808.

The previous prime is 1261217803. The next prime is 1261217819. The reversal of 1261217809 is 9087121621.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1234468225 + 26749584 = 35135^2 + 5172^2 .

It is a cyclic number.

It is not a de Polignac number, because 1261217809 - 2⁷ = 1261217681 is a prime.

It is not a weakly prime, because it can be changed into another prime (1261217803) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 630608904 + 630608905.

It is an arithmetic number, because the mean of its divisors is an integer number (630608905).

Almost surely, 2^1261217809 is an apocalyptic number.

It is an amenable number.

1261217809 is a deficient number, since it is larger than the sum of its proper divisors (1).

1261217809 is an equidigital number, since it uses as much as digits as its factorization.

1261217809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 12096, while the sum is 37.

The square root of 1261217809 is about 35513.6284966772. The cubic root of 1261217809 is about 1080.4301581515.

The spelling of 1261217809 in words is "one billion, two hundred sixty-one million, two hundred seventeen thousand, eight hundred nine".