4-wave sequence beginning with 2's with middles dropped.

Terms

a(0) =2a(1) =2a(2) =8a(3) =20a(4) =60a(5) =170a(6) =492a(7) =1414a(8) =4074a(9) =11728a(10) =33772a(11) =97240a(12) =279994a(13) =806208a(14) =2321386a(15) =6684162a(16) =19246280a(17) =55417452a(18) =159568196a(19) =459458306a(20) =1322957468a(21) =3809304206a(22) =10968454314a(23) =31582405472a(24) =90937912212a(25) =261845282320a(26) =753953441490