%I A101400
%S A101400 1,2,5,10,21,44,91,190,395,822,1711,3560,7409,15418,32085,66770,138949,
%T A101400 289156,601739,1252230,2605915,5422958,11285279,23484880,48872481,
%U A101400 101704562,211649125,440445850,916576181,1907412444,3969361531
%N A101400 a(n) = a(n - 1) + 2*a(n - 2) + a(n - 3) - a(n - 4)
%C A101400 Lengths of successive words (starting with a) under the substitution: 
               {a -> ab, b -> aac, c -> d, d -> b}.
%e A101400 a(0) = 1, a(1) = 2, a(2) = 5, a(3) = 10, a(4) = 21, a(5) = 44
%t A101400 a[0] = 1; a[1] = 2; a[2] = 5; a[3] = 10; a[n_] := a[n] = a[n - 1] + 2a[n 
               - 2] + a[n - 3] - a[n - 4]; Table[ a[n], {n, 0, 30}] (from Robert 
               G. Wilson v Jan 15 2005)
%Y A101400 Cf. A092886, A105309.
%Y A101400 Sequence in context: A101510 A066819 A114279 this_sequence A131403 A052540 
               A018106
%Y A101400 Adjacent sequences: A101397 A101398 A101399 this_sequence A101401 A101402 
               A101403
%K A101400 nonn,easy
%O A101400 0,2
%A A101400 J. F. J. Laros (jlaros(AT)liacs.nl), Jan 15 2005
%E A101400 More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 15 2005