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A184289
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Number of distinct n X 2 toroidal 0..5 arrays.
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2
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21, 351, 7826, 210456, 6047412, 181410426, 5597460306, 176319684486, 5642220380006, 182807931073356, 5982804736593846, 197432556035646576, 6560835699716880876, 219319364810710999926, 7369130657373455467336, 248708159686089506901366
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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]*6^(n*(k/LCM[c, d])), {d, Divisors[k]}], {c, Divisors[n]}]; a[n_] := T[n, 2]; Array[a, 16] (* Jean-François Alcover, Nov 01 2017, after Andrew Howroyd *)
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PROG
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(PARI) a(n) = my(k=2); (1/(n*k)) * sumdiv(n, c, sumdiv(k, d, eulerphi(c) * eulerphi(d) * 6^(n*k/lcm(c, d)))); \\ Michel Marcus, Nov 01 2017
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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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