Numbers k such that 4*10^k + 21 is prime.

Terms

a(0) =1a(1) =2a(2) =3a(3) =7a(4) =15a(5) =22a(6) =30a(7) =35a(8) =44a(9) =73a(10) =89a(11) =91a(12) =224a(13) =533a(14) =821a(15) =1037a(16) =1338a(17) =1458a(18) =1777a(19) =2046a(20) =2257a(21) =2877a(22) =3047a(23) =3407a(24) =13398a(25) =42766a(26) =55906a(27) =61625a(28) =66653a(29) =123113