(1/2)*A206803.

Terms

a(0) =1a(1) =4a(2) =13a(3) =26a(4) =49a(5) =78a(6) =121a(7) =188a(8) =264a(9) =370a(10) =498a(11) =638a(12) =804a(13) =1012a(14) =1265a(15) =1534a(16) =1854a(17) =2210a(18) =2585a(19) =3020a(20) =3497a(21) =4040a(22) =4675a(23) =5358a(24) =6066a(25) =6826a(26) =7613a(27) =8456a(28) =9502a(29) =10608