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 A353047 Number of length n words on alphabet {0,1,2} that contain each of the subwords 01, 02, 10, 12, 20, and 21 as (not necessarily contiguous) subwords. 1
 12, 108, 600, 2664, 10404, 37476, 127920, 420768, 1348476, 4242204, 13169160, 40490712, 123635028, 375623892, 1137095520, 3433306896, 10347106860, 31141984140, 93639862200, 281372571720, 845074016772, 2537235316548, 7615933808400, 22856659795584, 68588501433564 (list; graph; refs; listen; history; text; internal format)
 OFFSET 5,1 COMMENTS Let A be an alphabet containing m letters. Let S be the set of m^2-m ordered two-tuples of distinct letters in A. The generating function for the number of length n words on A that contain each two-tuple in S as a (not necessarily contiguous) subword is m*(m-1)!^2*x^(2*m-1)/((1-m*x)*Product_{k=1..m-1} (1-k*x)^2). Appears to equal 12 times A222993, except that sequence only has a conjectured formula. - N. J. A. Sloane, Jun 17 2022 LINKS Index entries for linear recurrences with constant coefficients, signature (9,-31,51,-40,12). FORMULA G.f.: (12*x^5)/((1 - 2*x)^2*(1 - x)^2*(1 - 3*x)). EXAMPLE a(5) = 12 because we have: {0, 1, 2, 0, 1}, {0, 1, 2, 1, 0}, {0, 2, 1, 0, 2}, {0, 2, 1, 2, 0}, {1, 0, 2, 0, 1}, {1, 0, 2, 1, 0}, {1, 2, 0, 1, 2}, {1, 2, 0, 2, 1}, {2, 0, 1, 0, 2}, {2, 0, 1, 2, 0}, {2, 1, 0, 1, 2}, {2, 1, 0, 2, 1}. MATHEMATICA nn = 15; vertices = Level[Outer[ List, {a, b, c}, {d, e, f}, {h, i, j}, {k, l, m}, {n, o, p}, {q, r, s}], {6}]; x = {a -> b, d -> e, i -> j, o -> p}; y = {b -> c, h -> i, k -> l, r -> s}; z = {e -> f, l -> m, n -> o, q -> r}; replacementlist = Table[vertices[[kk]] -> kk, {kk, 1, 729}]; G= Normal[SparseArray[Flatten[Table[Normal[Merge[ Map[{mm, vertices[[mm]] /. # /. replacementlist} -> 1 &, {x, y, z}], Total]], {mm, 1, 729}]]]]; Iwg = Inverse[IdentityMatrix[729] - w G]; CoefficientList[ Series[Iwg[[1, 729]], {w, 0, nn}], w] CROSSREFS Cf. A058809, A222993, A005803 (binary words). Sequence in context: A154671 A321672 A241230 * A037972 A111990 A053469 Adjacent sequences:  A353044 A353045 A353046 * A353048 A353049 A353050 KEYWORD nonn,easy AUTHOR Geoffrey Critzer, Apr 19 2022 STATUS approved

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Last modified August 7 23:50 EDT 2022. Contains 355995 sequences. (Running on oeis4.)