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A126286
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a(1) = 2, a(n) = n * LeastPrimeFactor(n+1) / LeastPrimeFactor(n).
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5
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2, 3, 2, 10, 2, 21, 2, 12, 6, 55, 2, 78, 2, 21, 10, 136, 2, 171, 2, 30, 14, 253, 2, 60, 10, 39, 18, 406, 2, 465, 2, 48, 22, 85, 14, 666, 2, 57, 26, 820, 2, 903, 2, 66, 30, 1081, 2, 168, 14, 75, 34, 1378, 2, 135, 22, 84, 38, 1711, 2, 1830, 2, 93, 42, 160, 26, 2211, 2, 102, 46
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OFFSET
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1,1
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LINKS
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FORMULA
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EXAMPLE
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a(6) = (6 / LeastPrimeFactor(6)) * LeastPrimeFactor(7) = 21.
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MATHEMATICA
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a[1] := 2; a[n_] := n*FactorInteger[n + 1][[1, 1]]/FactorInteger[n][[1, 1]]; Table[a[n], {n, 69}] (* Ivan Neretin, May 20 2015 *)
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PROG
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(PARI) a(n) = if (n==1, 2, n*factor(n+1)[1, 1]/factor(n)[1, 1]); \\ Michel Marcus, Aug 14 2013
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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