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A075020
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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.
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9
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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; internal format)
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OFFSET
| 1,2
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EXAMPLE
| a(4)= 29, 29 is the smallest prime divisor of 4321 =29*149
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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 (grafix(AT)csl.pl), Apr 04 2008
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CROSSREFS
| Cf. A075019.
Cf. A104759, A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138958, A138959, A138960, A138961, A138962.
Sequence in context: A080302 A080272 A098340 * A138962 A139206 A100651
Adjacent sequences: A075017 A075018 A075019 * A075021 A075022 A075023
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KEYWORD
| base,nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 01 2002
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EXTENSIONS
| More terms from Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de), Jan 03 2003
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