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A184289 Number of distinct n X 2 toroidal 0..5 arrays. 2
21, 351, 7826, 210456, 6047412, 181410426, 5597460306, 176319684486, 5642220380006, 182807931073356, 5982804736593846, 197432556035646576, 6560835699716880876, 219319364810710999926, 7369130657373455467336, 248708159686089506901366 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
MATHEMATICA
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 *)
PROG
(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
CROSSREFS
Column 2 of A184291.
Sequence in context: A299688 A300320 A271633 * A192093 A006105 A167032
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 10 2011
EXTENSIONS
Terms a(10) and beyond from Andrew Howroyd, Sep 27 2017
STATUS
approved

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Last modified September 30 21:59 EDT 2023. Contains 365812 sequences. (Running on oeis4.)