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A144852
a(n) = number of distinct prime divisors (taken together) of numbers of the form 4x^2+1 for x<=10^n.
0
9, 87, 836, 8000, 78124, 766585, 7556731, 74771106, 741554656, 7366252759, 73261462211, 729280694469
OFFSET
1,1
COMMENTS
Primes of the form 4x^2+1 see A121326(n) = A002496(n+1).
MATHEMATICA
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*)
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