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A280893
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a(n) is the maximum prime factor of the concatenation of all the previous terms, with a(1)=1, a(2)=2.
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2
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1, 2, 3, 41, 43, 1063, 5479, 111031, 790000148543, 790000148543, 326139075156576200419624217119, 326139075156576200419624217119, 326139075156576200419624217119, 246787955464079218902570922322710067417716295997334514692275780099917
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OFFSET
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1,2
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LINKS
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EXAMPLE
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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.
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MAPLE
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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);
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MATHEMATICA
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a = {1, 2}; Do[AppendTo[a, FactorInteger[FromDigits@ Flatten@ Map[IntegerDigits, a]][[-1, 1]]], {10}]; a (* Michael De Vlieger, Jan 10 2017 *)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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