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A060009 Ulam numbers starting with the numbers 1 and 9. 0
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

C. Pickover, Wonders of Numbers, Oxford University Press, NY, 2001, p. 185-186.

Cf. A002858

LINKS

Table of n, a(n) for n=1..60.

C. 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

AUTHOR

Jason Earls, Mar 16 2001

STATUS

approved

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Last modified July 10 02:05 EDT 2020. Contains 335570 sequences. (Running on oeis4.)