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%I #10 Jul 15 2012 10:02:17
%S 1,2,5,12,31,79,206,534,1396,3642,9530,24917,65221,170667,446780,
%T 1169467,3061621,8014862,20982965,54932637,143814946,376508559,
%U 985710731,2580614104,6756131581,17687755722,46307135585,121233585812
%N a(0) = 1, a(1) = 2; for n>0, a(2n) = 3a(2n-1) - a(2n-2), a(2n+1) = 3a(2n) - a(2n-1) - a(n-1).
%C Equals the eigensequence of the correlation triangle, A003983. (_Gary W. Adamson_, Mar 14, 2011).
%p a:=proc(n) if n=0 or n=1 then n+1 elif n mod 2 = 0 then 3*a(n-1)-a(n-2) else 3*a(n-1)-a(n-2)-a((n-3)/2) fi end: seq(a(n),n=0..30); - _Emeric Deutsch_, May 20 2007
%o (PARI) {m=27; v=vector(m+1); v[1]=1; v[2]=2; for(n=2, m, k=3*v[n]-v[n-1]; if(n%2==1, k=k-v[(n-1)/2]); v[n+1]=k); print(v)} /* Klaus Brockhaus, May 20 2007 */
%Y Cf. A003983
%K nonn
%O 0,2
%A _Paul Curtz_, May 19 2007
%E More terms from _Emeric Deutsch_ and _Klaus Brockhaus_, May 20 2007
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