Numbers k such that 5*10^k + 21 is prime.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =7a(5) =10a(6) =17a(7) =22a(8) =32a(9) =33a(10) =39a(11) =70a(12) =79a(13) =97a(14) =273a(15) =304a(16) =905a(17) =2474a(18) =3523a(19) =10348a(20) =15155a(21) =22252a(22) =22966a(23) =70858a(24) =82504a(25) =90793