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A129804
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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).
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Equals the eigensequence of the correlation triangle, A003983. (Gary W. Adamson, qntmpkt(AT)yahoo.com, Mar 14, 2011).
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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 (deutsch(AT)duke.poly.edu), May 20 2007
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PROG
| (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 */
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CROSSREFS
| Cf. A003983
Sequence in context: A112412 A193284 A125023 * A110035 A000635 A077556
Adjacent sequences: A129801 A129802 A129803 * A129805 A129806 A129807
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KEYWORD
| nonn
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AUTHOR
| Paul Curtz (bpcrtz(AT)free.fr), May 19 2007
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu) and Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), May 20 2007
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