A144851 a(n) = number of distinct prime divisors (taken together) of numbers of the form 2x^2+1 for x<=10^n.

8, 76, 760, 7445, 73477, 726948, 7218256, 71801859, 715087632, 7127665635, 71089166879, 709344259821

Offset

1,1

Links

Table of n, a(n) for n=1..12.

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

Mathematica

d = 10; l = 0; p = 2; 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*)

Crossrefs

Cf. A002383, A143835, A143868, A144848, A144850.

Sequence in context: A303736 A083234 A247744 * A233827 A231286 A251927

Adjacent sequences: A144848 A144849 A144850 * A144852 A144853 A144854

Keyword

nonn

Author

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

Extensions

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

Status

approved