a(n) = a(n-1) + 10*a(n-3) for n > 2; a(0) = a(1) = a(2) = 1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =11a(4) =21a(5) =31a(6) =141a(7) =351a(8) =661a(9) =2071a(10) =5581a(11) =12191a(12) =32901a(13) =88711a(14) =210621a(15) =539631a(16) =1426741a(17) =3532951a(18) =8929261a(19) =23196671a(20) =58526181a(21) =147818791a(22) =379785501a(23) =965047311a(24) =2443235221a(25) =6241090231a(26) =15891563341a(27) =40323915551a(28) =102734817861