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

7, 7, 19, 13, 31, 19, 43, 73, 109, 31, 67, 37, 79, 43, 181, 97, 103, 109, 229, 61, 127, 67, 139, 73, 151, 79, 163, 337, 349, 181, 373, 97, 199, 103, 211, 109, 223, 229, 937, 241, 739, 127, 1033, 397, 271, 139, 283, 433, 883, 151, 307, 157, 3181, 163, 331, 337

Offset: 1

Author

Amarnath Murthy, May 15 2002

Keywords

• nonn
• look

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A070846, A070848, A070849, A070850, A070851, A070852, A070853.

Cf. A034694.

Cf. A024892 (n such that a(n)=3*n+1).

Cf. A002476.

Programs

Maple

f:= proc(n) local k,d;
  if n::even then d:= 3*n else d:= 6*n fi;
  for k from 1 by d do if isprime(k) then return k fi od
end proc:
map(f, [$1..100]); # Robert Israel, Sep 19 2019

Mathematica

a[n_] := Module[{k, d}, If[EvenQ[n], d = 3n, d = 6n]; For[k = 1, True, k += d, If[PrimeQ[k], Return[k]]]];
Array[a, 100] (* Jean-François Alcover, Jun 11 2020, after Maple *)

PARI

for(n=1,80,s=1; while((isprime(s)*s-1)%(3*n)>0,s++); print1(s,","))

Extensions

More terms from Benoit Cloitre, May 18 2002