The number of unilevel points (unique points at their height) on Delannoy paths ending when x = n.

Terms

a(0) =1a(1) =4a(2) =8a(3) =20a(4) =48a(5) =116a(6) =280a(7) =676a(8) =1632a(9) =3940a(10) =9512a(11) =22964a(12) =55440a(13) =133844a(14) =323128a(15) =780100a(16) =1883328a(17) =4546756a(18) =10976840a(19) =26500436a(20) =63977712a(21) =154455860a(22) =372889432a(23) =900234724a(24) =2173358880a(25) =5246952484a(26) =12667263848a(27) =30581480180a(28) =73830224208a(29) =178241928596