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 A003666 a(n) is smallest number which is uniquely a(j)+a(k), j
 1, 4, 5, 6, 7, 8, 10, 16, 18, 19, 21, 31, 32, 33, 42, 46, 56, 57, 66, 70, 79, 82, 91, 96, 104, 105, 107, 116, 129, 130, 131, 141, 158, 165, 168, 179, 180, 182, 191, 204, 205, 206, 216, 217, 218, 219, 229, 230, 244, 256, 266, 267, 268, 281, 290, 315, 316, 317, 318, 328 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS An Ulam-type sequence - see A002858 for many further references, comments, etc. - T. D. Noe, Jan 21 2008 REFERENCES R. K. Guy, ``s-Additive sequences,'' preprint, 1994. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS T. D. Noe, Table of n, a(n) for n=1..10000 S. R. Finch, Patterns in 1-additive sequences, Experimental Mathematics 1 (1992), 57-63. R. K. Guy, s-Additive sequences, Preprint, 1994. (Annotated scanned copy) Eric Weisstein's World of Mathematics, Ulam Sequence Wikipedia, Ulam number MATHEMATICA Nest[Append[#, SelectFirst[Union@ Select[Tally@ Map[Total, Select[Permutations[#, {2}], #1 < #2 & @@ # &]], Last@ # == 1 &][[All, 1]], Function[k, FreeQ[#, k]]]] &, {1, 4}, 58] (* Michael De Vlieger, Nov 16 2017 *) PROG (Haskell) a003666 n = a003666_list !! (n-1) a003666_list = 1 : 4 : ulam 2 4 a003666_list -- Function ulam as defined in A002858. -- Reinhard Zumkeller, Nov 03 2011 CROSSREFS Cf. A003662, A199120, A199121. Sequence in context: A078778 A037356 A139199 * A295742 A047314 A298670 Adjacent sequences:  A003663 A003664 A003665 * A003667 A003668 A003669 KEYWORD nonn AUTHOR STATUS approved

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Last modified August 25 10:20 EDT 2019. Contains 326324 sequences. (Running on oeis4.)