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A117140
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a(1)=5, a(2)=7; for n >= 3, a(n) is smallest number which is uniquely of the form a(j)+a(k) with 1<=j<k<n.
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2
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5, 7, 12, 17, 19, 22, 26, 27, 32, 33, 36, 37, 40, 42, 46, 50, 56, 60, 66, 70, 71, 74, 81, 85, 91, 99, 101, 132, 138, 140, 150, 154, 156, 158, 160, 179, 181, 185, 189, 195, 205, 209, 233, 234, 236, 240, 248, 258, 264, 268, 287, 289, 293, 297, 303, 336, 340, 342, 348
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| An Ulam-type sequence - see A002858 for many further references, comments, etc.
Does not seem to have any nice periodicity like A007300 does. - Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), May 24 2006
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..10000
A. N. Debono, Ulam Sequences
Eric Weisstein's World of Mathematics, Ulam Sequence
Wikipedia, Ulam number
Index entries for Ulam numbers
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MATHEMATICA
| max=100; A117140 = {5, 7}; Do[ AppendTo[ A117140, n = Last[A117140]; While[n++; Length[ DeleteCases[ Intersection[A117140, n - A117140], n/2, 1, 1]] != 2]; n], {max}]; A117140 (* From Jean-François Alcover, Nov 30 2011 *)
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PROG
| (Haskell)
a117140 n = a117140_list !! (n-1)
a117140_list = 5 : 7 : ulam 2 7 a117140_list
-- Function ulam as defined in A002858.
-- Reinhard Zumkeller, Nov 03 2011
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CROSSREFS
| Sequence in context: A086255 A171490 A047382 * A031144 A160243 A020686
Adjacent sequences: A117137 A117138 A117139 * A117141 A117142 A117143
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Apr 29 2006
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EXTENSIONS
| More terms from Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), May 24 2006
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