

A117140


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.


2



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
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OFFSET

1,1


COMMENTS

An Ulamtype sequence  see A002858 for many further references, comments, etc.
Does not seem to have any nice periodicity like A007300 does.  Joshua Zucker, May 24 2006


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


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 (* JeanFrançois Alcover, Nov 30 2011 *)


PROG

(Haskell)
a117140 n = a117140_list !! (n1)
a117140_list = 5 : 7 : ulam 2 7 a117140_list
 Function ulam as defined in A002858.
 Reinhard Zumkeller, Nov 03 2011


CROSSREFS

Sequence in context: A314308 A314309 A314310 * A263536 A314311 A031144
Adjacent sequences: A117137 A117138 A117139 * A117141 A117142 A117143


KEYWORD

nonn


AUTHOR

N. J. A. Sloane, Apr 29 2006


EXTENSIONS

More terms from Joshua Zucker, May 24 2006


STATUS

approved



