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 A177726 Number of line segments connecting exactly 10 points in an n x n grid of points 0
 0, 0, 0, 0, 0, 0, 0, 0, 0, 22, 52, 90, 136, 190, 252, 322, 400, 486, 620, 770, 936, 1118, 1316, 1530, 1760, 2006, 2268, 2662, 3088, 3546, 4036, 4558, 5112, 5698, 6316, 6966, 7800, 8682, 9612, 10590, 11616, 12690, 13812, 14982, 16200, 17842, 19564, 21366 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,10 COMMENTS a(n) is also the number of pairs of points visible to each other exactly through 8 points in an n x n grid of points. LINKS FORMULA See Mathematica code. MATHEMATICA j=9; a[n_]:=a[n]=If[n<=j, 0, 2*a1[n]-a[n-1]+R1[n]] a1[n_]:=a1[n]=If[n<=j, 0, 2*a[n-1]-a1[n-1]+R2[n]] R1[n_]:=R1[n]=If[n<=j, 0, R1[n-1]+4*S[n]] R2[n_]:=(n-1)*S[n] S[n_]:=If[Mod[n-1, j]==0, EulerPhi[(n-1)/j], 0] Table[a[n], {n, 1, 50}] CROSSREFS Sequence in context: A200880 A111576 A277979 * A101571 A290381 A324486 Adjacent sequences:  A177723 A177724 A177725 * A177727 A177728 A177729 KEYWORD nonn AUTHOR Seppo Mustonen, May 13 2010 STATUS approved

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Last modified October 19 21:28 EDT 2019. Contains 328244 sequences. (Running on oeis4.)