%I A051800
%S A051800 1,2,3,4,5,11,18,23,26,30,80,120,148,220
%N A051800 Numbers n such that 1 + double of product of first n primes is also a 
               prime.
%e A051800 5 is a member because 2*(2*3*5*7*11)+1=4621 is prime
%Y A051800 2*A002110[n]+1 is prime. Cf. A051887, A051915.
%Y A051800 Sequence in context: A116068 A104420 A052418 this_sequence A121432 A118968 
               A073528
%Y A051800 Adjacent sequences: A051797 A051798 A051799 this_sequence A051801 A051802 
               A051803
%K A051800 nonn
%O A051800 1,2
%A A051800 Labos E. (labos(AT)ana.sote.hu), Dec 20 1999