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 A005244 A self-generating sequence: start with 2 and 3, take all products of any 2 previous elements, subtract 1 and adjoin them to the sequence. (Formerly M0704) 6
 2, 3, 5, 9, 14, 17, 26, 27, 33, 41, 44, 50, 51, 53, 65, 69, 77, 80, 81, 84, 87, 98, 99, 101, 105, 122, 125, 129, 131, 134, 137, 149, 152, 153, 158, 159, 161, 164, 167, 173, 194, 195, 197, 201, 204, 206, 209, 219, 230, 233, 237, 239, 242, 243, 249 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n) = A139127(n)*a(k)-1 for some k; A139128 gives number of distinct representations a(n) = a(i)*a(j)-1. - Reinhard Zumkeller, Apr 09 2008 Complement of A171413. [Jaroslav Krizek, Dec 08 2009] REFERENCES R. K. Guy, Unsolved Problems in Number Theory, E31. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 Eric Weisstein's World of Mathematics, Hofstadter Sequences. EXAMPLE 17 is present because it equals 2*9-1. MATHEMATICA f[s_, mx_] := Union[s, Select[Apply[Times, Subsets[s, {2}], {1}] - 1, # <= mx &]]; mx = 250; FixedPoint[f[#, mx] &, {2, 3}] (* From Jean-François Alcover , Mar 29 2011 *) PROG (Haskell) import Data.Set (singleton, deleteFindMin, fromList, union) a005244 n = a005244_list !! (n-1) a005244_list = f [2] (singleton 2) where    f xs s = y :      f (y : xs) (s' `union` fromList (map ((subtract 1) . (* y)) xs))      where (y, s') = deleteFindMin s -- Reinhard Zumkeller, Feb 26 2013 CROSSREFS Cf. A139127, A139128, A171413. Sequence in context: A220315 A070819 A195667 * A058541 A023672 A023567 Adjacent sequences:  A005241 A005242 A005243 * A005245 A005246 A005247 KEYWORD nonn,nice,easy AUTHOR D. R. Hofstadter EXTENSIONS More terms from Jud McCranie STATUS approved

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Last modified January 26 22:05 EST 2022. Contains 350601 sequences. (Running on oeis4.)