A364367 An irregular triangle read by rows, the 4th row-symmetric Fibonaccian triangle: T(n,k) is the Whitney number of level k of the (4,n)-th symmetric Fibonaccian lattice (0 <= n, 0 <= k <= 3*n).
1, 1, 1, 1, 1, 1, 2, 3, 3, 3, 2, 1, 1, 3, 6, 8, 10, 10, 8, 6, 3, 1, 1, 4, 10, 17, 25, 31, 33, 31, 25, 17, 10, 4, 1, 1, 5, 15, 31, 53, 77, 98, 110, 110, 98, 77, 53, 31, 15, 5, 1, 1, 6, 21, 51, 100, 166, 242, 313, 364, 383, 364, 313, 242, 166, 100, 51, 21, 6, 1
Offset: 0
Examples
Triangle T(n,k) (with rows n >= 0 and columns k >= 0) starts as follows: 1; 1, 1, 1, 1; 1, 2, 3, 3, 3, 2, 1; 1, 3, 6, 8, 10, 10, 8, 6, 3, 1; 1, 4, 10, 17, 25, 31, 33, 31, 25, 17, 10, 4, 1; 1, 5, 15, 31, 53, 77, 98, 110, 110, 98, 77, 53, 31, 15, 5, 1; ... Below are the 15 (4,2) Fibonaccian strings (organized by rank level) that comprise the (4,2)nd symmetric Fibonaccian lattice: rank=6: (1,5) rank=5: (1,6) (2,5) rank=4: (1,7) (2,6) (3,5) rank=3: (1,8) (2,7) (3,6) rank=2: (2,8) (3,7) (4,6) rank=1: (3,8) (4,7) rank=0: (4,8) The pair (4,5) is disallowed as a (4,2) Fibonaccian string since it contains consecutive integers. In the (4,3)rd symmetric Fibonaccian lattice, rank level 5 consists of exactly the (4,3) Fibonaccian strings whose coordinate sum is 4*(3*(3+1)/2)-5=19: (1,6,12), (1,7,11), (1,8,10), (2,5,12), (2,6,11), (2,7,10), (3,5,11), (3,6,10), (3,7,9), and (4,6,9), confirming that T(3,5)=10.
Links
- R. G. Donnelly, M. W. Dunkum, M. L. Huber, and L. Knupp, "Sign-alternating Gibonacci polynomials", arXiv:2012.14993 [math.CO], 2020.
- R. G. Donnelly, M. W. Dunkum, M. L. Huber, and L. Knupp, "Sign-alternating Gibonacci polynomials", Enumer. Comb. Appl. 1:2 (2021), art. id. S2R15.
- R. G. Donnelly and M. W. Dunkum, "Gelfand--Tsetlin-type weight bases for all special linear Lie algebra representations corresponding to skew Schur functions", arXiv:2012.14986 [math.CO], 2020-2022.
- R. G. Donnelly and M. W. Dunkum, "Gelfand--Tsetlin-type weight bases for all special linear Lie algebra representations corresponding to skew Schur functions", Adv. Appl. Math. 139 (2022), art. id. 102356.
- R. G. Donnelly, M. W. Dunkum, S. V. Lišková, and A. Nance, "Symmetric Fibonaccian distributive lattices and representations of the special linear Lie algebras", arXiv:2012.14991 [math.CO], 2020-2022.
- R. G. Donnelly, M. W. Dunkum, S. V. Lišková, and A. Nance, "Symmetric Fibonaccian distributive lattices and representations of the special linear Lie algebras", Involve 16:2 (2023), 201-226.
Formula
With T(0,0)=1, then T(n,k) = T(n-1,k-3) + T(n-1,k-2) + T(n-1,k-1) + T(n-1,k) - T(n-2,k-3) for n >= 1 and 0 <= k <= 3*n, understanding T(i,j) to be zero when j < 0 or j > 3*i. That the preceding recurrence holds is equivalent to the identity p(n,x) = (1+x+x^2+x^3)*p(n-1,x) - x^3*p(n-2,x) for n >= 1, where p(0,x)=1 and p(-1,x) is taken to be 0.
Comments