Largest prime <= 6^n.

Terms

a(0) =5a(1) =31a(2) =211a(3) =1291a(4) =7759a(5) =46649a(6) =279919a(7) =1679609a(8) =10077689a(9) =60466169a(10) =362796997a(11) =2176782317a(12) =13060693999a(13) =78364164083a(14) =470184984569