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 A048489 a(n) = 7 * 2^n - 6. 10
 1, 8, 22, 50, 106, 218, 442, 890, 1786, 3578, 7162, 14330, 28666, 57338, 114682, 229370, 458746, 917498, 1835002, 3670010, 7340026, 14680058, 29360122, 58720250, 117440506, 234881018, 469762042, 939524090, 1879048186 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Number of 3 X n 0-1 matrices avoiding simultaneously the right angled numbered polyomino patterns (ranpp) (00;1), (10;0) and (11;0). An occurrence of a ranpp (xy;z) in a matrix A=(a(i,j)) is a triple (a(i1,j1), a(i1,j2), a(i2,j1)) where i10, a(0)=1. - Vincenzo Librandi, Aug 06 2010 G.f.: ( 1+5*x ) / ( (2*x-1)*(x-1) ). - R. J. Mathar, Oct 21 2012 a(n) = A063757(2*n). - Philippe Deléham, Apr 13 2013 MAPLE A048489:=n->7*2^n-6: seq(A048489(n), n=0..40); # Wesley Ivan Hurt, Apr 18 2017 MATHEMATICA CoefficientList[Series[(1 + 5 x)/((2 x - 1) (x - 1)), {x, 0, 28}], x] (* Michael De Vlieger, May 22 2018 *) 7*2^Range[0, 30]-6 (* or *) LinearRecurrence[{3, -2}, {1, 8}, 30] (* Harvey P. Dale, May 19 2019 *) PROG (PARI) a(n)=7<

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Last modified February 16 15:17 EST 2020. Contains 331961 sequences. (Running on oeis4.)