A369871 a(n) = least prime factor of A024411(n).
2, 2, 3, 2, 3, 2, 2, 3, 2, 3, 2, 5, 2, 3, 3, 2, 2, 5, 3, 2, 2, 3, 5, 2, 2, 2, 3, 2, 3, 5, 2, 7, 2, 3, 2, 3, 2, 7, 3, 2, 2, 3, 5, 3, 2, 2, 5, 2, 3, 2, 7, 2, 3, 2, 2, 5, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 2, 3, 7, 2, 5, 3, 2, 3, 5, 2, 7, 3, 2, 3, 2, 3, 2, 5, 2, 3
Offset: 1
Keywords
Examples
Factorizations of for the first four terms of A024411 are given by 20 = 2 * 2 * 5; 28 = 2 * 2 * 7; 33 = 3 * 13; 36 = 2*2*3*3; so that (a(1), a(2), a(3), a(4)) = (2, 2, 3, 2). Corner of array whose n-th row shows the numbers n such that a(n) = n-th prime: 1 2 4 6 7 9 11 3 5 8 10 14 15 19 12 18 23 30 43 47 56 32 38 51 69 77 94 107
Programs
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Mathematica
readOEISbFile[bNumber_] := ToExpression[ToString[Map[StringReplace[#, FromCharacterCode[32] -> FromCharacterCode[44]] &, Map[Most[#] &, Cases[Map[{#, StringFreeQ[StringTake[#, 1], Except[Apply[Alternatives, Flatten[{Map[ToString[#] &, Range[10] - 1], FromCharacterCode[45], FromCharacterCode[8722], "+"}]]]]} &, Map[StringDrop[StringDrop[#, 1], -1] &, DeleteCases[ Map[ToString[{#}] &, Import[If[Head[bNumber] === Integer, "http://oeis.org/" <> "A" <> # <> "/b" <> # <> ".txt" &[ StringTrim[StringReplace[ToString[PadLeft[IntegerDigits[bNumber], 6]], FromCharacterCode[{44, 32}] -> ""], "{" | "}"]], bNumber], "List"]], "{}"]]], {_, True}]]]]] s = readOEISbFile["http://oeis.org/A024411/b024411.txt"]; (* s = 10000 terms of A024411 from b-file *) t = Map[Last, s]; u = Take[t, 1000]; f[n_] := FactorInteger[n][[1, 1]]; Join[{1}, Array[f, 120, 2]]; v = Map[f, u] (* Peter J. C. Moses, Feb 03 2024 *)
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