a(n) = Sum_{k=0..n} T(n,k), where T is the array defined in A025177.

Terms

a(0) =1a(1) =1a(2) =4a(3) =11a(4) =33a(5) =97a(6) =288a(7) =855a(8) =2544a(9) =7577a(10) =22590a(11) =67399a(12) =201215a(13) =601017a(14) =1795966a(15) =5368659a(16) =16053417a(17) =48015873a(18) =143649102a(19) =429842511a(20) =1286452725a(21) =3850770081a(22) =11528245602a(23) =34517105907a(24) =103360732956a(25) =309543786441a(26) =927106804368