a(n) = a(n-1) + a(n-2) + 4, with a(0)=0, a(1)=2.

Terms

a(0) =0a(1) =2a(2) =6a(3) =12a(4) =22a(5) =38a(6) =64a(7) =106a(8) =174a(9) =284a(10) =462a(11) =750a(12) =1216a(13) =1970a(14) =3190a(15) =5164a(16) =8358a(17) =13526a(18) =21888a(19) =35418a(20) =57310a(21) =92732a(22) =150046a(23) =242782a(24) =392832a(25) =635618a(26) =1028454a(27) =1664076a(28) =2692534a(29) =4356614