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A085688
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a(1) = 11; a(n) = if n == 2 mod 3 then a(n-1)-3, if n == 0 mod 3 then a(n-1)-2, if n == 1 mod 3 then a(n-1)*2.
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1
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11, 8, 6, 12, 9, 7, 14, 11, 9, 18, 15, 13, 26, 23, 21, 42, 39, 37, 74, 71, 69, 138, 135, 133, 266, 263, 261, 522, 519, 517, 1034, 1031, 1029, 2058, 2055, 2053, 4106, 4103, 4101, 8202, 8199, 8197, 16394, 16391, 16389, 32778, 32775, 32773, 65546, 65543, 65541, 131082
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Sequence (in reversed order) was given as a puzzle: find the next term after 18, 9, 11, 14, 7, 9, 12! Thanks to Farideh Firoozbakht and Zak Seidov for the solution.
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FORMULA
| a[1]=11; for k=>1, a[3k-1]=7+2^(3k-1), a[3k]=5+2^(3k-1), a[3k+1]=10+2^(3k). - zakirs(AT)yosh.ac.il, Jul 24, 2003
a(n) = 2^floor((n-1)/3) + floor(21/(((n-1) mod 3)+2)). - Dean Hickerson, Jul 24, 2003
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MAPLE
| a := proc(n) option remember; if n=1 then 11 elif n mod 3 = 2 then a(n-1)-3 elif n mod 3 = 0 then a(n-1)-2 else a(n-1)*2; fi; end;
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MATHEMATICA
| a[1] = 11; a[n_] := (3 - (-1)^mod[n, 3])/2*a[n - 1] - (1 + (-1)^mod[n, 3])/2* Floor[mod[n, 3]/2] - (-1)^mod[n, 3] - 1 (from Farideh Firoozbakht (f.firoozbakht(AT)sci.ui.ac.ir), Jul 23 2003)
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CROSSREFS
| Sequence in context: A090841 A085757 A003567 * A164059 A171250 A068974
Adjacent sequences: A085685 A085686 A085687 * A085689 A085690 A085691
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Jul 18 2003
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