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A089328
Smallest prime of the form the concatenation r*k for r = 1 to n followed by a 1.
2
11, 241, 1231, 71421281, 2468101, 246810121, 244872961201441681, 8162432404856641, 1234567891, 10320630941251561872182492710301, 12345678910111, 12243648607284961081201321441, 43861291722152583013443874304735165591, 9418828237647056465875284694010341128122213161, 214263841051261471681892102312522732943151
OFFSET
1,1
LINKS
EXAMPLE
a(3) = 1231 and k = 1.
MAPLE
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:
map(f, [$1..20]); # Robert Israel, Apr 30 2018
CROSSREFS
Cf. A089329.
Sequence in context: A296170 A264465 A090921 * A077422 A361143 A377451
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Nov 04 2003
EXTENSIONS
More terms from David Wasserman, Sep 13 2005
STATUS
approved