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A153339 Number of zig-zag paths from top to bottom of a rectangle of width 5 with n rows whose color is that of the top right corner 2
3, 4, 8, 12, 24, 36, 72, 108, 216, 324, 648, 972, 1944, 2916, 5832, 8748, 17496, 26244, 52488, 78732, 157464, 236196, 472392, 708588, 1417176, 2125764, 4251528, 6377292, 12754584, 19131876, 38263752, 57395628, 114791256, 172186884 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Indranil Ghosh, Table of n, a(n) for n = 1..4182

Joseph Myers, BMO 2008--2009 Round 1 Problem 1---Generalisation

Index entries for linear recurrences with constant coefficients, signature (0,3).

FORMULA

a(2n) = 4*3^(n-1), a(2n+1) = 8*3^(n-1) for n>0,  a(1)=3.

a(n) = 3*a(n-2) for n>3. G.f.: x*(3+4*x-x^2)/(1-3*x^2). [Colin Barker, May 10 2012]

MATHEMATICA

a[1]=3; a[2]=4; a[3]=8; a[n_]:=3 a[n-2]; Table[a[n], {n, 1, 34}] (* or *) LinearRecurrence[{0, 3}, {3, 4, 8}, 34] (* Indranil Ghosh, Feb 20 2017 *)

CROSSREFS

Sequence in context: A074331 A052952 A245121 * A275989 A033955 A049720

Adjacent sequences:  A153336 A153337 A153338 * A153340 A153341 A153342

KEYWORD

easy,nonn

AUTHOR

Joseph Myers, Dec 24 2008

STATUS

approved

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Last modified April 20 22:22 EDT 2019. Contains 322310 sequences. (Running on oeis4.)