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A280893 a(n) is the maximum prime factor of the concatenation of all the previous terms, with a(1)=1, a(2)=2. 1
1, 2, 3, 41, 43, 1063, 5479, 111031, 790000148543, 790000148543, 326139075156576200419624217119, 326139075156576200419624217119, 326139075156576200419624217119, 246787955464079218902570922322710067417716295997334514692275780099917 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Hans Havermann, Table of n, a(n) for n = 1..15

EXAMPLE

The maximum prime factor of concat(1,2) = 12 is 3, so a(3) = 3;

The maximum prime factor of concat(1,2,3) = 123 is 41, so a(4) = 41; etc.

MAPLE

with(numtheory): P:= proc(q) local a, b, c, k, n; print(1); print(2); a:=12; for n from 3 to q do b:=ifactors(a)[2]; c:=0; for k from 1 to nops(b) do if b[k][1]>c then c:=b[k][1]; fi; od; a:=a*10^(ilog10(c)+1)+c; print(c); od; end: P(10^2);

MATHEMATICA

a = {1, 2}; Do[AppendTo[a, FactorInteger[FromDigits@ Flatten@ Map[IntegerDigits, a]][[-1, 1]]], {10}]; a (* Michael De Vlieger, Jan 10 2017 *)

CROSSREFS

Cf. A280894.

Sequence in context: A059800 A330293 A302687 * A215508 A215385 A215389

Adjacent sequences:  A280890 A280891 A280892 * A280894 A280895 A280896

KEYWORD

nonn,base

AUTHOR

Paolo P. Lava, Jan 10 2017

EXTENSIONS

a(12)-a(13) from Jon E. Schoenfield, Jan 10 2017

a(14)-a(15) from Hans Havermann, Jan 12 2017

STATUS

approved

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Last modified July 11 18:01 EDT 2020. Contains 335649 sequences. (Running on oeis4.)