Number of tree polyominoes with width 3 and height n.

Terms

a(0) =1a(1) =10a(2) =55a(3) =243a(4) =980a(5) =3789a(6) =14357a(7) =53832a(8) =200723a(9) =746163a(10) =2769272a(11) =10268745a(12) =38059769a(13) =141027852a(14) =522497759a(15) =1935672399a(16) =7170707492a(17) =26563347645a(18) =98400786941a(19) =364511817696