A smoothed version of A091587.

Terms

a(0) =1a(1) =3a(2) =8a(3) =24a(4) =67a(5) =195a(6) =580a(7) =1730a(8) =5179a(9) =15533a(10) =46578a(11) =139712a(12) =419115a(13) =1257319a(14) =3771930a(15) =11315764a(16) =33947261a(17) =101841751a(18) =305525228a(19) =916575642a(20) =2749726883