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 A138960 a(n) = smallest prime divisor of A138957(n). 7
 1, 2, 3, 2, 3, 2, 127, 2, 3, 857, 3, 3, 18503, 3, 3, 43, 3, 3, 17, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 7, 3, 3, 1051, 3, 3, 67103, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 5, 3, 3, 5, 3, 3, 5, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For largest prime divisors see A138961. LINKS MATHEMATICA a = {}; b = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[Length[w] - k + 1]]], {k, 1, Length[w]}]; p = FromDigits[a]; AppendTo[b, First[First[FactorInteger[p]]]], {n, 1, 38}]; b A137957[n_] := FromDigits[Flatten[Reverse /@ IntegerDigits[Range[n]]]]; Table[FactorInteger[A137957[n]][[1, 1]], {n, 39}] (* Robert Price, May 10 2019 *) CROSSREFS Cf. A104759, A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138958, A138961. Sequence in context: A251089 A119880 A075019 * A245553 A115397 A218656 Adjacent sequences:  A138957 A138958 A138959 * A138961 A138962 A138963 KEYWORD nonn,base AUTHOR Artur Jasinski, Apr 04 2008 EXTENSIONS a(39)-a(69) from Robert Price, May 10 2019 STATUS approved

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Last modified July 20 14:23 EDT 2019. Contains 325185 sequences. (Running on oeis4.)