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A070847 Smallest prime == 1 mod (3n).

%I A070847 #19 Jun 11 2020 15:34:52
%S A070847 7,7,19,13,31,19,43,73,109,31,67,37,79,43,181,97,103,109,229,61,127,
%T A070847 67,139,73,151,79,163,337,349,181,373,97,199,103,211,109,223,229,937,
%U A070847 241,739,127,1033,397,271,139,283,433,883,151,307,157,3181,163,331,337
%N A070847 Smallest prime == 1 mod (3n).
%H A070847 Robert Israel, <a href="/A070847/b070847.txt">Table of n, a(n) for n = 1..10000</a>
%p A070847 f:= proc(n) local k,d;
%p A070847   if n::even then d:= 3*n else d:= 6*n fi;
%p A070847   for k from 1 by d do if isprime(k) then return k fi od
%p A070847 end proc:
%p A070847 map(f, [$1..100]); # _Robert Israel_, Sep 19 2019
%t A070847 a[n_] := Module[{k, d}, If[EvenQ[n], d = 3n, d = 6n]; For[k = 1, True, k += d, If[PrimeQ[k], Return[k]]]];
%t A070847 Array[a, 100] (* _Jean-François Alcover_, Jun 11 2020, after Maple *)
%o A070847 (PARI) for(n=1,80,s=1; while((isprime(s)*s-1)%(3*n)>0,s++); print1(s,","))
%Y A070847 Cf. A070846, A070848, A070849, A070850, A070851, A070852, A070853.
%Y A070847 Cf. A034694.
%Y A070847 Cf. A024892 (n such that a(n)=3*n+1).
%Y A070847 Cf. A002476.
%K A070847 nonn,look
%O A070847 1,1
%A A070847 _Amarnath Murthy_, May 15 2002
%E A070847 More terms from _Benoit Cloitre_, May 18 2002