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 A075020 a(1) = 1; for n>1, a(n) = the smallest prime divisor of the number C(n) formed from the reverse concatenation of 1,2,3,... up to n. 9
 1, 3, 3, 29, 3, 3, 19, 3, 3, 7, 3, 3, 17, 3, 3, 23, 3, 3, 17, 3, 3, 13, 3, 3, 11, 3, 3, 23, 3, 3, 7, 3, 3, 89, 3, 3, 29, 3, 3, 11, 3, 3, 52433, 3, 3, 23, 3, 3, 71, 3, 3, 7, 3, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS EXAMPLE a(4)= 29, 29 is the smallest prime divisor of 4321 =29*149 MATHEMATICA b = {}; a = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[Length[w] - k + 1]]], {k, 1, Length[w]}]; p = FromDigits[Reverse[a]]; AppendTo[b, First[First[FactorInteger[p]]]], {n, 1, 21}]; b - Artur Jasinski, Apr 04 2008 CROSSREFS Cf. A075019. Cf. A104759, A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138958, A138959, A138960, A138961, A138962. Sequence in context: A215829 A098340 A271938 * A138962 A139206 A100651 Adjacent sequences:  A075017 A075018 A075019 * A075021 A075022 A075023 KEYWORD base,nonn AUTHOR Amarnath Murthy, Sep 01 2002 EXTENSIONS More terms from Sascha Kurz, Jan 03 2003 STATUS approved

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Last modified October 19 13:01 EDT 2019. Contains 328222 sequences. (Running on oeis4.)