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A026427
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a(n) = least positive integer > a(n-1) and not equal to a(i)*a(j) for 1<=i<=j<=n.
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3
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3, 4, 5, 6, 7, 8, 10, 11, 13, 14, 17, 19, 22, 23, 26, 27, 29, 31, 34, 37, 38, 41, 43, 45, 46, 47, 53, 54, 58, 59, 61, 62, 63, 67, 71, 72, 73, 74, 75, 79, 82, 83, 86, 89, 90, 94, 96, 97, 99, 101, 103, 105, 106, 107, 109, 113, 117, 118, 120, 122, 125, 126, 127, 128, 131, 134
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OFFSET
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1,1
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COMMENTS
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Starting from 3, include only those numbers that aren't the product of two numbers already included.
Numbers >3 not included: 9,12,15,18,21,24,30,33,39,42,51,57,66,69,78,....
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LINKS
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EXAMPLE
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9 is excluded because 9=3*3. 10 is included because 10 is not the product of any two of 3,4,5,6,7,8.
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MATHEMATICA
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f[s_List] := Block[{k = s[[ -1]] + 1, ss = Times @@@ Tuples[s, 2]}, While[MemberQ[ss, k], k++ ]; Append[s, k]]; Nest[f, {3}, 65] (* Robert G. Wilson v Sep 23 2006 *)
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CROSSREFS
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Cf. A026416 and references therein.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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