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A153371
Number of zig-zag paths from top to bottom of a rectangle of width 11 with 2n rows whose color is that of the top right corner.
4
10, 36, 132, 488, 1812, 6744, 25132, 93720, 349620, 1304504, 4867884, 18166008, 67794100, 253006296, 944222892, 3523868888, 13151219892, 49080945144, 183172429612, 683608511160, 2551261090740, 9521434803224, 35534476025004
OFFSET
1,1
FORMULA
Empirical: G.f. -2*x*(5-12*x+3*x^2) / ( (2*x-1)*(x^2-4*x+1) ) with a(n)= +6*a(n-1) -9*a(n-2) +2*a(n-3) and a(n) = (2^n+4*A001075(n+1))/3. - R. J. Mathar, Jun 16 2011
KEYWORD
easy,nonn
AUTHOR
Joseph Myers, Dec 24 2008
STATUS
approved