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Search: id:A122280
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| A122280 |
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a(1) = 1, a(2) = 2; for n >= 3, a(n) = the smallest positive integer not occurring earlier in the sequence such that GCD(a(n-1),a(n)) is a prime. |
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+0
3
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| 1, 2, 4, 6, 3, 9, 12, 10, 5, 15, 18, 8, 14, 7, 21, 24, 22, 11, 33, 27, 30, 16, 26, 13, 39, 36, 34, 17, 51, 42, 20, 25, 35, 28, 38, 19, 57, 45, 40, 46, 23, 69, 48, 50, 32, 54, 44, 55, 60, 58, 29, 87, 63, 49, 56, 62, 31, 93, 66, 52, 65, 70, 64, 74, 37, 111, 72, 75, 78, 68, 82, 41
(list; graph; listen)
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OFFSET
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1,2
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MATHEMATICA
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f[s_] := Block[{k = 1}, While[MemberQ[s, k] || ! PrimeQ[GCD[Last[s], k]], k++ ]; Append[s, k] ]; Nest[f, {1, 2}, 75] (*Chandler*)
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CROSSREFS
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Cf. A122281.
Sequence in context: A026218 A096665 A064413 this_sequence A057063 A002849 A072984
Adjacent sequences: A122277 A122278 A122279 this_sequence A122281 A122282 A122283
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Aug 29 2006
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EXTENSIONS
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Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net) and Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Aug 30 2006
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