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 A089328 Smallest prime of the form the concatenation r*k for r = 1 to n followed by a 1. 2

%I

%S 11,241,1231,71421281,2468101,246810121,244872961201441681,

%T 8162432404856641,1234567891,10320630941251561872182492710301,

%U 12345678910111,12243648607284961081201321441,43861291722152583013443874304735165591,9418828237647056465875284694010341128122213161,214263841051261471681892102312522732943151

%N Smallest prime of the form the concatenation r*k for r = 1 to n followed by a 1.

%H Robert Israel, <a href="/A089328/b089328.txt">Table of n, a(n) for n = 1..187</a>

%e a(3) = 1231 and k = 1.

%p dcat:= proc(L) local t,i;

%p t:= L[1];

%p for i from 2 to nops(L) do

%p t:= t*10^(1+ilog10(L[i]))+L[i]

%p od:

%p t

%p end proc:

%p f:= proc(n) local r,k,p;

%p for k from 1 do

%p p:= dcat([seq(r*k,r=1..n),1]);

%p if isprime(p) then return p fi

%p od

%p end proc:

%p map(f, [\$1..20]); # _Robert Israel_, Apr 30 2018

%Y Cf. A089329.

%K base,nonn

%O 1,1

%A _Amarnath Murthy_, Nov 04 2003

%E More terms from _David Wasserman_, Sep 13 2005

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Last modified January 27 21:49 EST 2023. Contains 359849 sequences. (Running on oeis4.)