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%I #12 Jun 30 2015 11:12:28
%S 9,87,836,8000,78124,766585,7556731,74771106,741554656,7366252759,
%T 73261462211,729280694469
%N a(n) = number of distinct prime divisors (taken together) of numbers of the form 4x^2+1 for x<=10^n.
%C Primes of the form 4x^2+1 see A121326(n) = A002496(n+1).
%H Bernhard Helmes, <a href="http://www.devalco.de/quadr_Sieb_4x%5E2+1.php#4a">Prime sieving on the polynomial f(n)=4n^2+1</a>.
%t d = 10; l = 0; p = 4; 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_*)
%Y Cf. A002383, A121326, A143835, A143868, A144848, A144850, A144851.
%K nonn
%O 1,1
%A _Artur Jasinski_ & Bernhard Helmes (bhelmes(AT)gmx.de), Sep 22 2008
%E Fixed broken link, corrected and extended to agree with website. - _Ray Chandler_, Jun 30 2015