Number of "forceless" (or "useless") sequences in n-column Nonogram puzzle.

Terms

a(0) =0a(1) =1a(2) =1a(3) =3a(4) =3a(5) =7a(6) =8a(7) =15a(8) =20a(9) =33a(10) =47a(11) =75a(12) =110a(13) =172a(14) =259a(15) =401a(16) =612a(17) =947a(18) =1457a(19) =2258a(20) =3494a(21) =5428a(22) =8434a(23) =13138a(24) =20480a(25) =31982a(26) =49991a(27) =78244a(28) =122583a(29) =192255