First differences are A005563.

Terms

a(0) =1a(1) =4a(2) =12a(3) =27a(4) =51a(5) =86a(6) =134a(7) =197a(8) =277a(9) =376a(10) =496a(11) =639a(12) =807a(13) =1002a(14) =1226a(15) =1481a(16) =1769a(17) =2092a(18) =2452a(19) =2851a(20) =3291a(21) =3774a(22) =4302a(23) =4877a(24) =5501a(25) =6176a(26) =6904a(27) =7687a(28) =8527a(29) =9426