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A144852
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a(n) = number of distinct prime divisors (taken together) of numbers of the form 4x^2+1 for x<=10^n.
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0
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9, 87, 836, 8000, 78124, 766585, 7556731, 74771106, 741554656, 7366252759, 73261462211, 729280694469
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OFFSET
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1,1
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COMMENTS
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Primes of the form 4x^2+1 see A121326(n) = A002496(n+1).
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LINKS
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Table of n, a(n) for n=1..12.
Bernhard Helmes, Prime sieving on the polynomial f(n)=4n^2+1.
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MATHEMATICA
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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*)
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CROSSREFS
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Cf. A002383, A121326, A143835, A143868, A144848, A144850, A144851.
Sequence in context: A100814 A055725 A219123 * A153191 A223277 A267265
Adjacent sequences: A144849 A144850 A144851 * A144853 A144854 A144855
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KEYWORD
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nonn
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AUTHOR
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Artur Jasinski & Bernhard Helmes (bhelmes(AT)gmx.de), Sep 22 2008
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EXTENSIONS
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Fixed broken link, corrected and extended to agree with website. - Ray Chandler, Jun 30 2015
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STATUS
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approved
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