%I A091859
%S A091859 2,5,31,311,3733,59729,1194581,57339889,1605516893,22477236503,
%T A091859 1933042339259,143045133105167,2574812395893007,87543621460362239,
%U A091859 700348971682897913,58829313621363424693,1411903526912722192633
%N A091859 a(1) = 2, a(n) is the least prime of the form 2k*a(n-1)+1 where 2k is 
               the least even number not used earlier.
%e A091859 a(2) = 5 = 2*2+1, But a(3) = 31 though 11= 5*2 +1 is also prime.
%o A091859 Contribution from Rick L. Shepherd (rshepherd2(AT)hotmail.com), Sep 08 
               2009: (Start)
%o A091859 (PARI) {a=[2]; terms=1; used=Set();
%o A091859 while(terms<30, k2=0; until(isprime(k2*a[terms]+1),
%o A091859 until(setsearch(used,k2)==0, k2=k2+2));
%o A091859 a=concat(a,k2*a[terms]+1); terms++; used=setunion(used,Set([k2]))); a} 
               (End)
%Y A091859 Sequence in context: A058009 A097396 A056788 this_sequence A085873 A051048 
               A163852
%Y A091859 Adjacent sequences: A091856 A091857 A091858 this_sequence A091860 A091861 
               A091862
%K A091859 nonn
%O A091859 1,1
%A A091859 Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Mar 13 2004
%E A091859 a(6) onwards by Rick L. Shepherd (rshepherd2(AT)hotmail.com), Sep 08 
               2009