A075022 - OEIS

A075022

a(1) = 1; for n>1, a(n) = the largest prime divisor of the number C(n) formed from the concatenation of 1,2,3,... up to n.

1, 3, 41, 617, 823, 643, 9721, 14593, 3803, 1234567891, 630803, 2110805449, 869211457, 205761315168520219, 8230452606740808761, 1231026625769, 584538396786764503, 801309546900123763, 833929457045867563

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OFFSET

1,2

LINKS

N. J. A. Sloane, Table of n, a(n) for n = 1..56 [First 50 terms from Zak Seidov]

EXAMPLE

a(4) = 617 since 1234 = 2*617.

MATHEMATICA

a = {}; b = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[k]]], {k, 1, Length[w]}]; p = FromDigits[a]; AppendTo[b, First[Last[FactorInteger[p]]]], {n, 1, 25}]; b (* Artur Jasinski, Apr 04 2008 *)

Table[FactorInteger[FromDigits[Flatten[IntegerDigits/@Range[n]]]][[-1, 1]], {n, 20}] (* Harvey P. Dale, Aug 31 2015 *)

CROSSREFS

Cf. A075019, A075020, A075021.

Cf. A104759, A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138960, A138961, A138962.

Sequence in context: A155672 A073844 A138961 * A367981 A300281 A012175

Adjacent sequences: A075019 A075020 A075021 * A075023 A075024 A075025

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Sep 01 2002

EXTENSIONS

More terms from Sascha Kurz, Jan 03 2003

STATUS

approved