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Here is the table:

$\begin{array}{c} 0\\ 1\\ 1& 1\\ 3& 2& 3\\ 5& 3& 3& 5\\ 11 &8 &10 &8 &11\\ 21 &13 &14 &14 &13 &21\\ 43 &30 &37 &36 &37 &30 &43\\ 85 &55 &61 &55 &55 &61 &55 &85\\ 171 &116 &140 &140 &146 &140 &140 &116 &171 \end{array}$

In this triangle like table, I am unable to find the relation between columnwise. Say for 1st column, I have found the relation $A(n)= A(n-1)+2A(n-2)$.

For the 2nd column, I have the relation $A(n)= A(n-1)+2A(n-2) + x$ [ where $x$ is $-1$ for even row number and $+1$ for odd].

But for other columns, I have not found the relations yet. Can anyone help me find a generalized equation to generate the table?

  • 1
    The first column and the diagonal appear to be [A001045](http://oeis.org/A001045), $J_n = \frac{2^n-(-1)^n}{3}$. [Wikipedia has an article](https://en.wikipedia.org/wiki/Jacobsthal_number), too.2012-10-08

1 Answers 1

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Updated: let $A(n,k)$ be the number in the table with row $n$ and column $k$, where $0\le n$ and $0\le k\le n$.

$A(n,k)=A(n,n-k)$ $A(n,0)=A(n,n)=0$

The table would look like this: (top left is row $0$ and column $0$)

$\begin{array}{c} 0\\ 0& 0\\ 0& 1& 0\\ 0& 1& 1& 0\\ 0& 3& 2& 3& 0\\ 0& 5& 3& 3& 5& 0\\ 0& 11 &8 &10 &8 &11& 0\\ 0& 21 &13 &14 &14 &13 &21& 0\\ 0& 43 &30 &37 &36 &37 &30 &43& 0\\ 0& 85 &55 &61 &55 &55 &61 &55 &85& 0\\ 0& 171 &116 &140 &140 &146 &140 &140 &116 &171 & 0 \end{array}$

Then, we have: $A(n+1,k)+A(n,k)+A(n,k-1)=2^{n-1}$


Example $A(8,3)+A(7,3)+A(7,2)=37+14+13=64=2^6$

  • 0
    @EmmadKareem Is it better now?2012-10-09