a(n) = (1/4)*A291732(n).

Terms

a(0) =1a(1) =3a(2) =9a(3) =26a(4) =72a(5) =195a(6) =520a(7) =1368a(8) =3560a(9) =9184a(10) =23520a(11) =59860a(12) =151536a(13) =381840a(14) =958256a(15) =2396192a(16) =5972736a(17) =14845040a(18) =36801792a(19) =91021056a(20) =224642304a(21) =553347072a(22) =1360598016a(23) =3340024384a(24) =8186748160a(25) =20038426368a(26) =48983457024a(27) =119593531904a(28) =291657627648a(29) =710522702592