A261356 Pyramid of coefficients in expansion of (1+x+2*y)^n.
1, 1, 1, 2, 1, 2, 4, 1, 4, 4, 1, 3, 6, 3, 12, 12, 1, 6, 12, 8, 1, 4, 8, 6, 24, 24, 4, 24, 48, 32, 1, 8, 24, 32, 16, 1, 5, 10, 10, 40, 40, 10, 60, 120, 80, 5, 40, 120, 160, 80, 1, 10, 40, 80, 80, 32, 1, 6, 12, 15, 60, 60, 20, 120, 240, 160, 15, 120, 360, 480
Offset: 0
Examples
Here is the fourth (n=3) slice of the pyramid: .....1...... ...3 6.... ..3 12 12. .1 6 12 8 As an irregular triangle, rows begin: 1; 1, 1, 2; 1, 2, 4, 1, 4, 4; 1, 3, 6, 3, 12, 12, 1, 6, 12, 8; ...
Links
- Alois P. Heinz, Rows n = 0..38, flattened
Programs
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Maple
p:= proc(i, j, k) option remember; if k<0 or i<0 or i>k or j<0 or j>i then 0 elif {i, j, k}={0} then 1 else p(i, j, k-1) +p(i-1, j, k-1) +2*p(i-1, j-1, k-1) fi end: seq(seq(seq(p(i, j, k), j=0..i), i=0..k), k=0..5); # Alois P. Heinz, Aug 20 2015
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Mathematica
p[i_, j_, k_] := p[i, j, k] = If[k < 0 || i < 0 || i > k || j < 0 || j > i, 0, If[Union@{i, j, k} == {0}, 1, p[i, j, k - 1] + p[i - 1, j, k - 1] + 2* p[i - 1, j - 1, k - 1]]]; Table[Table[Table[p[i, j, k], {j, 0, i}], {i, 0, k}], {k, 0, 5}] // Flatten (* Jean-François Alcover, Sep 16 2023, after Alois P. Heinz *)
Formula
T(i+1,j,k) = 2*T(i,j-1,k-1)+T(i,j-1,k)+T(i,j,k); T(i,j,-1)=0,...; T(0,0,0)=1.
T(n,j,k) = 2^k*binomial(n,j)*binomial(j,k). - Dimitri Boscainos, Aug 21 2015
Comments