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A060009
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Ulam numbers starting with the numbers 1 and 9.
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1
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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)
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OFFSET
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1,2
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REFERENCES
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Clifford A. Pickover, Wonders of Numbers, Oxford University Press, NY, 2001, p. 185-186.
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LINKS
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Clifford A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review.
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FORMULA
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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.
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EXAMPLE
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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.
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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