A144848 a(n) = number of distinct prime divisors (taken together) of numbers of the form x^2+1 for x<=10^n.

7, 70, 720, 7102, 70780, 704537, 7026559, 70122424, 700184485, 6993568566, 69870544960, 698175242376

Offset: 1

Author

Artur Jasinski & Bernhard Helmes (bhelmes(AT)gmx.de), Sep 22 2008, Sep 24 2008

Keywords

• nonn

Links

• Bernhard Helmes, Prime sieving on the polynomial f(n)=n^2+1.

Crossrefs

For primes of the form n^2+1 see A002496.

Cf. A002496, A143835, A143868, A144850, A144851.

Programs

Mathematica

d = 10; l = 0; p = 1; c = {}; a = {}; Do[k = p x^2 + 1; b = Divisors[k]; Do[If[PrimeQ[b[[n]]], AppendTo[a, b[[n]]]], {n, 1, Length[b]}]; If[x == d, a = Union[a]; l = Length[a]; d = 10 d; Print[l]; AppendTo[c, l]], {x, 1, 10000}]; c (* Artur Jasinski *)

Extensions

Fixed broken link and extended to agree with website. - Ray Chandler, Jun 30 2015