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 A075021 a(1) = 1; for n>1, a(n) = the largest prime divisor of the number C(n) formed from the reverse concatenation of 1,2,3,... up to n. 7
 1, 7, 107, 149, 953, 218107, 402859, 4877, 379721, 54421, 370329218107, 5767189888301, 237927839, 1728836281, 136133374970881, 1190788477118549, 677181889, 399048049, 40617114482123, 629639170774346584751 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS EXAMPLE a(4)= 149 as 149 is the largest 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[Last[FactorInteger[p]]]], {n, 1, 21}]; b - Artur Jasinski, Apr 04 2008 CROSSREFS Cf. A075019, A075020, A075022. Cf. A104759, A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138958, A138959, A138960, A138961, A138962. Sequence in context: A213863 A231899 A188407 * A138963 A141932 A002687 Adjacent sequences:  A075018 A075019 A075020 * A075022 A075023 A075024 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 June 24 09:54 EDT 2019. Contains 324323 sequences. (Running on oeis4.)