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Search: id:A125065
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| A125065 |
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a(1)=1. a(n) is the smallest positive integer not occurring earlier in the sequence such that a(n)/GCD(a(n),a(n-1)) is not a prime. |
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+0
1
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| 1, 4, 2, 8, 9, 3, 10, 5, 6, 16, 15, 12, 25, 14, 7, 18, 20, 21, 22, 11, 24, 27, 26, 13, 28, 30, 32, 33, 34, 17, 35, 36, 40, 39, 38, 19, 42, 44, 45, 46, 23, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 29, 60, 63, 62, 31, 64, 65, 66, 68, 69, 70, 72, 75, 74, 37, 76, 77, 78, 80, 81, 82
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Sequence is a permutation of the positive integers.
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EXAMPLE
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a(22) = 27 because 27 is the smallest positive integer not occurring among the first 21 terms of the sequence such that a(22)/GCD(a(22),a(21)) = 27/GCD(27, 24) = 9 is not a prime.
a(8) = 5 because 5 is the smallest positive integer not occurring among the 1st 7 terms of the sequence such that a(8)/GCD(a(8),a(7)) = 5/GCD(5,10) = 1 is not a prime.
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MATHEMATICA
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f[l_List] := Block[{k = 1}, While[MemberQ[l, k] || PrimeQ[k/GCD[k, l[[ -1]]]], k++ ]; Append[l, k]]; Nest[f, {1}, 72] (*Chandler*)
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CROSSREFS
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Sequence in context: A098798 A131783 A094312 this_sequence A109816 A050128 A134042
Adjacent sequences: A125062 A125063 A125064 this_sequence A125066 A125067 A125068
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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), Jan 09 2007
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EXTENSIONS
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Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Feb 13 2007
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