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 A060009 Ulam numbers starting with the numbers 1 and 9. 1
 1, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 36, 38, 39, 40, 41, 42, 43, 44, 46, 66, 67, 68, 69, 70, 71, 72, 73, 92, 101, 121, 122, 123, 124, 125, 126, 127, 146, 155, 174, 182, 201, 211, 229, 230, 237, 256, 284, 285, 286, 287, 288, 289, 290, 291, 311, 348, 365, 368 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES Clifford A. Pickover, Wonders of Numbers, Oxford University Press, NY, 2001, p. 185-186. LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 Clifford A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review. FORMULA Ulam numbers are positive integers that can be expressed in just one way as the sum of two distinct earlier members of the sequence in increasing order. EXAMPLE a(4) = 11 is an Ulam number because 10 + 1 = 11, but 19 is not because there is more than one way to form 19 from summing previous sequence numbers, e.g., 18 + 1 and 10 + 9. CROSSREFS Cf. A002858. Sequence in context: A107043 A182362 A023392 * A250042 A115843 A058365 Adjacent sequences:  A060006 A060007 A060008 * A060010 A060011 A060012 KEYWORD nonn,base AUTHOR Jason Earls, Mar 16 2001 STATUS approved

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Last modified November 28 22:15 EST 2021. Contains 349415 sequences. (Running on oeis4.)