A225812 Irregular triangle read by rows: T(n,k) is the number of binary pattern classes in the (4,n)-rectangular grid with k '1's and (4n-k) '0's: two patterns are in same class if one of them can be obtained by a reflection or 180-degree rotation of the other.
1, 1, 2, 4, 2, 1, 1, 2, 10, 14, 22, 14, 10, 2, 1, 1, 4, 22, 60, 139, 208, 252, 208, 139, 60, 22, 4, 1, 1, 4, 36, 140, 476, 1092, 2044, 2860, 3270, 2860, 2044, 1092, 476, 140, 36, 4, 1, 1, 6, 56, 294, 1253, 3912, 9808, 19464, 31706, 42116, 46448, 42116, 31706
Offset: 0
Examples
Irregular triangle: 1 1 2 4 2 1 1 2 10 14 22 14 10 2 1 1 4 22 60 139 208 252 208 139 60 22 4 1 1 4 36 140 476 1092 2044 2860 3270 2860 2044 1092 476 140 36 4 1 ...
Links
- Yosu Yurramendi and María Merino, Rows n = 0..26 of irregular triangle, flattened
Programs
-
Mathematica
T[n_, k_] := (Binomial[4n, k] + If[EvenQ[k], 2 Binomial[2n, k/2], 0] + Sum[Binomial[4 Mod[n, 2], k - 2i] Binomial[4 Quotient[n, 2], i], {i, 0, Quotient[k, 2]}])/4; Table[T[n, k], {n, 0, 5}, {k, 0, 4n}] // Flatten (* Jean-François Alcover, Oct 06 2017, after Andrew Howroyd *)
-
PARI
T(n,k)={(binomial(4*n,k) + if(k%2==0,2*binomial(2*n,k/2),0) + sum(i=0,k\2,binomial(4*(n%2),k-2*i)*binomial(4*(n\2),i)))/4} for(n=0,4,for(k=0,4*n, print1(T(n,k), ", "));print) \\ Andrew Howroyd, May 30 2017
Extensions
Definition corrected by María Merino, May 19 2017
Comments