a(n) = a(n-1) + 2*a(n-3) with a(0)=a(1)=1, a(2)=3.

Terms

a(0) =1a(1) =1a(2) =3a(3) =5a(4) =7a(5) =13a(6) =23a(7) =37a(8) =63a(9) =109a(10) =183a(11) =309a(12) =527a(13) =893a(14) =1511a(15) =2565a(16) =4351a(17) =7373a(18) =12503a(19) =21205a(20) =35951a(21) =60957a(22) =103367a(23) =175269a(24) =297183a(25) =503917a(26) =854455a(27) =1448821a(28) =2456655a(29) =4165565