Number of (1,1) steps starting at level zero in all peakless Motzkin paths of length n+3.

Terms

a(0) =1a(1) =3a(2) =7a(3) =17a(4) =41a(5) =98a(6) =235a(7) =565a(8) =1362a(9) =3294a(10) =7992a(11) =19450a(12) =47475a(13) =116204a(14) =285178a(15) =701585a(16) =1730003a(17) =4275162a(18) =10586164a(19) =26263365a(20) =65273566a(21) =162499838a(22) =405185762a(23) =1011815774a(24) =2530219435a(25) =6335642377a(26) =15884284791a(27) =39871297479a(28) =100194076029