A129804 a(0) = 1, a(1) = 2; for n>0, a(2*n) = 3*a(2*n-1) - a(2*n-2), a(2*n+1) = 3*a(2*n) - a(2*n-1) - a(n-1).

1, 2, 5, 12, 31, 79, 206, 534, 1396, 3642, 9530, 24917, 65221, 170667, 446780, 1169467, 3061621, 8014862, 20982965, 54932637, 143814946, 376508559, 985710731, 2580614104, 6756131581, 17687755722, 46307135585, 121233585812

Offset: 0

Author

Paul Curtz, May 19 2007

Keywords

• nonn
• changed

Comments

Equals the eigensequence of the correlation triangle, A003983. - Gary W. Adamson, Mar 14 2011

Crossrefs

Cf. A003983.

Programs

Maple

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

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 */

Extensions

More terms from Emeric Deutsch and Klaus Brockhaus, May 20 2007