First lower diagonal of Parker's triangle A047812.

Terms

a(0) =0a(1) =1a(2) =3a(3) =7a(4) =11a(5) =18a(6) =26a(7) =38a(8) =52a(9) =73a(10) =97a(11) =131a(12) =172a(13) =227a(14) =293a(15) =381a(16) =486a(17) =623a(18) =788a(19) =998a(20) =1251a(21) =1571a(22) =1954a(23) =2432a(24) =3006a(25) =3714a(26) =4561a(27) =5600a(28) =6838a(29) =8345