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A089328
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Smallest prime of the form the concatenation r*k for r = 1 to n followed by a 1.
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2
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11, 241, 1231, 71421281, 2468101, 246810121, 244872961201441681, 8162432404856641, 1234567891, 10320630941251561872182492710301, 12345678910111, 12243648607284961081201321441, 43861291722152583013443874304735165591, 9418828237647056465875284694010341128122213161, 214263841051261471681892102312522732943151
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(3) = 1231 and k = 1.
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MAPLE
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dcat:= proc(L) local t, i;
t:= L[1];
for i from 2 to nops(L) do
t:= t*10^(1+ilog10(L[i]))+L[i]
od:
t
end proc:
f:= proc(n) local r, k, p;
for k from 1 do
p:= dcat([seq(r*k, r=1..n), 1]);
if isprime(p) then return p fi
od
end proc:
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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