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A184273
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Number of distinct n X 2 toroidal 0..3 arrays.
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2
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10, 76, 700, 8296, 104968, 1399176, 19175140, 268447816, 3817763740, 54975738736, 799645010860, 11728126132976, 173215372864600, 2573485530115576, 38430716856090160, 576460752706084936, 8680820741074491040, 131176846752106589576, 1988364834899715824380
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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T[n_, k_] := (1/(n*k))*Sum[Sum[EulerPhi[c]*EulerPhi[d]*4^(n*k/LCM[c, d]), {d, Divisors[k]}], {c, Divisors[n]}]; a[n_] := T[n, 2]; Array[a, 20] (* Jean-François Alcover, Oct 31 2017, after Andrew Howroyd *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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