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Search: id:A075021
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| A075021 |
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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. |
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+0
8
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| 1, 7, 107, 149, 953, 218107, 402859, 4877, 379721, 54421, 370329218107, 5767189888301, 237927839, 1728836281, 136133374970881, 1190788477118549, 677181889, 399048049, 40617114482123, 629639170774346584751
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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a(4)= 149 as 149 is the largest prime divisor of 4321 =29*149
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MATHEMATICA
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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 (grafix(AT)csl.pl), Apr 04 2008
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CROSSREFS
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Cf. A075019, A075020, A075022.
Cf. A104759, A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138958, A138959, A138960, A138961, A138962.
Sequence in context: A002486 A141358 A141362 this_sequence A138963 A141932 A002687
Adjacent sequences: A075018 A075019 A075020 this_sequence A075022 A075023 A075024
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KEYWORD
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base,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 01 2002
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EXTENSIONS
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More terms from Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de), Jan 03 2003
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