a(n) = A154798(n)/2.

Terms

a(0) =1a(1) =11a(2) =21a(3) =501a(4) =1218a(5) =1859a(6) =2802a(7) =6155a(8) =18669a(9) =26587a(10) =52779a(11) =102113a(12) =357610a(13) =650078a(14) =870815a(15) =1161760a(16) =2043984a(17) =3544750a(18) =6066082a(19) =7898238a(20) =13271830a(21) =17131481a(22) =46334860a(23) =59057152a(24) =75099068a(25) =95284646a(26) =192138168a(27) =241751422a(28) =303581873a(29) =380501078