Mersenne prime indices that are also Gaussian primes.

Terms

a(0) =3a(1) =7a(2) =19a(3) =31a(4) =107a(5) =127a(6) =607a(7) =1279a(8) =2203a(9) =4423a(10) =86243a(11) =110503a(12) =216091a(13) =756839a(14) =1257787a(15) =20996011a(16) =24036583a(17) =25964951a(18) =37156667