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A184290 Number of distinct n X 3 toroidal 0..5 arrays. 2

%I #17 Nov 01 2017 12:23:47

%S 76,7826,1119936,181402676,31345666736,5642220395616,1044616697187576,

%T 197432555854243976,37907050706575921296,7369130657373455467336,

%U 1447029292717527455513576,286511799958073253432316896,57126045037793735333314420176

%N Number of distinct n X 3 toroidal 0..5 arrays.

%H Andrew Howroyd, <a href="/A184290/b184290.txt">Table of n, a(n) for n = 1..100</a>

%t 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, 3]; Array[a, 13] (* _Jean-Fran├žois Alcover_, Nov 01 2017, after _Andrew Howroyd_ *)

%o (PARI) a(n) = my(k=3); (1/(n*k)) * sumdiv(n, c, sumdiv(k, d, eulerphi(c) * eulerphi(d) * 6^(n*k/lcm(c, d)))); \\ _Michel Marcus_, Nov 01 2017

%Y Column 3 of A184291.

%K nonn

%O 1,1

%A _R. H. Hardin_, Jan 10 2011

%E Terms a(7) and beyond from _Andrew Howroyd_, Sep 27 2017

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Last modified February 21 12:17 EST 2024. Contains 370235 sequences. (Running on oeis4.)