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 A255623 Number of length n+1 0..2 arrays with at most two downsteps in every n consecutive neighbor pairs. 1
 9, 27, 81, 237, 651, 1647, 3834, 8272, 16698, 31824, 57720, 100296, 167898, 272034, 428247, 657153, 985663, 1448409, 2089395, 2963895, 4140621, 5704185, 7757880, 10426806, 13861368, 18241174, 23779362, 30727386, 39380292, 50082516, 63234237 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Row 1 of A255622. LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = (1/40320)*n^8 + (11/10080)*n^7 + (7/576)*n^6 + (7/180)*n^5 + (847/5760)*n^4 + (1007/1440)*n^3 + (1237/672)*n^2 + (913/280)*n + 3. Empirical g.f.: x*(9 - 54*x + 162*x^2 - 276*x^3 + 300*x^4 - 216*x^5 + 99*x^6 - 26*x^7 + 3*x^8) / (1 - x)^9. - Colin Barker, Jan 21 2018 EXAMPLE Some solutions for n=4: ..0....1....2....1....2....2....2....0....2....1....2....0....1....2....1....0 ..0....0....0....1....0....0....0....1....0....2....2....0....1....1....2....0 ..1....1....0....2....2....0....1....0....0....0....0....2....1....0....0....0 ..2....1....1....0....0....1....0....0....1....2....2....2....1....0....1....2 ..1....0....2....1....2....1....1....0....0....1....0....1....0....1....0....2 CROSSREFS Cf. A255622. Sequence in context: A053702 A036314 A215690 * A036317 A053762 A126322 Adjacent sequences:  A255620 A255621 A255622 * A255624 A255625 A255626 KEYWORD nonn AUTHOR R. H. Hardin, Feb 28 2015 STATUS approved

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Last modified January 28 06:29 EST 2020. Contains 331317 sequences. (Running on oeis4.)