Triangle read by rows: T(n,k) = number of permutations of {1..n} with at most k inversions.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =1a(5) =3a(6) =5a(7) =6a(8) =1a(9) =4a(10) =9a(11) =15a(12) =20a(13) =23a(14) =24a(15) =1a(16) =5a(17) =14a(18) =29a(19) =49a(20) =71a(21) =91a(22) =106a(23) =115a(24) =119a(25) =120a(26) =1a(27) =6a(28) =20a(29) =49