Search: id:A105423
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%I A105423
%S A105423 1,0,3,3,9,15,31,57,108,199,366,666,1205,2166,3873,6891,12207,21537,
%T A105423 37859,66327,115842,201743,350412,607140,1049545,1810428,3116655,
%U A105423 5355219,9185349,15728547,26890375,45904773,78253896,133221079
%N A105423 Number of compositions of n+2 having exactly two parts equal to 1.
%C A105423 Column 2 of A105422.
%F A105423 G.f.=(1-z)^3/(1-z-z^2)^3.
%F A105423 (1/50) [(5n^2+21n+25)*Lucas(n) - (11n^2+30n+10)*Fibonacci(n) ]. - Ralf 
               Stephan, Jun 1 2007
%e A105423 a(4)=9 because we have (1,1,4),(1,4,1),(4,1,1),(1,1,2,2),(1,2,1,2),(1,
               2,2,1),(2,1,1,2),(2,1,2,1) and (2,2,1,1).
%p A105423 G:=(1-z)^3/(1-z-z^2)^3: Gser:=series(G,z=0,42): 1,seq(coeff(Gser,z^n),
               n=1..40);
%Y A105423 Cf. A105422.
%Y A105423 Sequence in context: A138383 A052436 A122847 this_sequence A147471 A166265 
               A062510
%Y A105423 Adjacent sequences: A105420 A105421 A105422 this_sequence A105424 A105425 
               A105426
%K A105423 nonn
%O A105423 0,3
%A A105423 Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 07 2005

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