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A143868
a(n)= Number of distinct prime divisors (taken together) of numbers of the form 2x^2-1 for x<=10^n.
4
8, 84, 815, 7922, 77250, 759077, 7492588, 74198995, 736401956, 7319543972, 72834161468, 725344237597
OFFSET
1,1
MATHEMATICA
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[N[Log[x]/Log[10]] == Round[N[Log[x]/Log[10]]], a = Union[a]; l = Length[a]; Print[l]; AppendTo[c, l]], {x, 1, 10000}]; c (*Artur Jasinski*)
CROSSREFS
Cf. A143835.
Sequence in context: A039939 A199907 A264710 * A130591 A166483 A048665
KEYWORD
nonn
AUTHOR
Artur Jasinski, Sep 04 2008
EXTENSIONS
Fixed broken link and corrected terms to agree with website - Ray Chandler, Jun 30 2015
STATUS
approved