Twin lucky numbers (upper terms).

Terms

a(0) =3a(1) =9a(2) =15a(3) =33a(4) =51a(5) =69a(6) =75a(7) =129a(8) =135a(9) =171a(10) =195a(11) =237a(12) =261a(13) =285a(14) =321a(15) =393a(16) =429a(17) =477a(18) =489a(19) =519a(20) =537a(21) =579a(22) =615a(23) =621a(24) =645a(25) =729a(26) =741a(27) =885a(28) =897a(29) =927