Array read by downwards antidiagonals: sigma_k(n) for n >= 1, k >= 0.

Terms

a(0) =1a(1) =2a(2) =1a(3) =2a(4) =3a(5) =1a(6) =3a(7) =4a(8) =5a(9) =1a(10) =2a(11) =7a(12) =10a(13) =9a(14) =1a(15) =4a(16) =6a(17) =21a(18) =28a(19) =17a(20) =1a(21) =2a(22) =12a(23) =26a(24) =73a(25) =82a(26) =33a(27) =1a(28) =4a(29) =8