Triangle arising from (4,2) tennis ball problem, read by rows.

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =1a(5) =4a(6) =10a(7) =16a(8) =22a(9) =1a(10) =6a(11) =21a(12) =52a(13) =105a(14) =158a(15) =211a(16) =1a(17) =8a(18) =36a(19) =116a(20) =301a(21) =644a(22) =1198a(23) =1752a(24) =2306a(25) =1a(26) =10a(27) =55a(28) =216a(29) =678