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%I #15 Nov 09 2020 06:25:03
%S 11,341,13981,852841,60551711,6115722811,801159688241,120975112924391,
%T 21896495439314771,4182230628909121261,882450662699824586071,
%U 212670609710657725243111,53380323037375089036020861
%N Product of first n primes that end in 1.
%H Robert Israel, <a href="/A092609/b092609.txt">Table of n, a(n) for n = 1..286</a>
%e a(1)= 11 = 11
%e a(2)= 11*31 = 341
%e a(3)= 11*31*41= 13981
%e a(4)= 11*31*41*61= 852841
%p Res:= NULL: p:= 1: count:= 0:
%p for n from 11 by 10 while count < 30 do
%p if isprime(n) then count:= count+1; p:= p*n; Res:= Res,p fi
%p od:
%p Res; # _Robert Israel_, Sep 16 2018
%t Rest[FoldList[Times,1,Select[Prime[Range[70]],Mod[#,10]==1&]]] (* _Harvey P. Dale_, Jun 05 2013 *)
%o (PARI) a(n) = {my(k=1, x=1); for (j=1, n, while(!isprime(10*k+1), k++); x *= (10*k+1); k++;); x;} \\ _Michel Marcus_, Nov 09 2020
%Y Cf. A030430.
%K nonn,easy
%O 1,1
%A _Jorge Coveiro_, Apr 11 2004
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