Number of hairpin compositions of n.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =2a(5) =4a(6) =14a(7) =28a(8) =70a(9) =140a(10) =310a(11) =621a(12) =1302a(13) =2607a(14) =5335a(15) =10675a(16) =21593