Variant of Lucas numbers: a(n) = a(n-1) + 4*a(n-2) starting with a(0)=2 and a(1)=1.

Terms

a(0) =2a(1) =1a(2) =9a(3) =13a(4) =49a(5) =101a(6) =297a(7) =701a(8) =1889a(9) =4693a(10) =12249a(11) =31021a(12) =80017a(13) =204101a(14) =524169a(15) =1340573a(16) =3437249a(17) =8799541a(18) =22548537a(19) =57746701a(20) =147940849a(21) =378927653a(22) =970691049a(23) =2486401661a(24) =6369165857a(25) =16314772501a(26) =41791435929a(27) =107050525933a(28) =274216269649a(29) =702418373381