3rd-largest term in n-th row of Stern's diatomic triangle A002487.

Terms

a(0) =1a(1) =3a(2) =5a(3) =11a(4) =18a(5) =30a(6) =49a(7) =80a(8) =129a(9) =209a(10) =338a(11) =547a(12) =885a(13) =1432a(14) =2317a(15) =3749a(16) =6066a(17) =9815a(18) =15881a(19) =25696a(20) =41577a(21) =67273a(22) =108850a(23) =176123a(24) =284973a(25) =461096a(26) =746069a(27) =1207165a(28) =1953234a(29) =3160399