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Math Help - Closed form of a sequence

  1. #1
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    Crna Gora
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    Closed form of a sequence

    If :

    \begin{cases}  a(4)=2 \\  a(8)=50 \\  a(12)=102 \\a(20)=1104 \end{cases}

    what is  a(n) ?
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  2. #2
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    Re: Closed form of a sequence

    You haven't defined a sequence. You've only given a few terms.

    You could use Lagrange interpolation to get a polynomial:

    a_n=2\frac{(n-8)(n-12)(n-20)}{(4-8)(4-12)(4-20)}+....
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