Number of compositions of n with exactly 3 adjacent equal parts.

Terms

a(0) =1a(1) =0a(2) =2a(3) =8a(4) =13a(5) =28a(6) =72a(7) =150a(8) =311a(9) =678a(10) =1428a(11) =2864a(12) =5912a(13) =12102a(14) =24168a(15) =48448a(16) =96599a(17) =190544a(18) =375276a(19) =736086a(20) =1435046a(21) =2788930a(22) =5402468a(23) =10424094a(24) =20053479a(25) =38470242a(26) =73582008a(27) =140379426a(28) =267176911a(29) =507295558