Triangle T(n,k) = Sum_{d|k} phi(d)*n^(k/d).

Terms

a(0) =1a(1) =2a(2) =6a(3) =3a(4) =12a(5) =33a(6) =4a(7) =20a(8) =72a(9) =280a(10) =5a(11) =30a(12) =135a(13) =660a(14) =3145a(15) =6a(16) =42a(17) =228a(18) =1344a(19) =7800a(20) =46956a(21) =7a(22) =56a(23) =357a(24) =2464a(25) =16835a(26) =118104a(27) =823585a(28) =8a(29) =72