Question

I have been challenged to find the general term or the recurrence relation for this sequence

5,18,44,96,195.... The only hint I have is that this sequence is an applied Fibonacci sequence. Can someone please suggest ways to find the recurrence or the nth term. I have looked at OEIS but found no note this for this particular integer sequence. I have searched at numerous locations but have had no success. Also ,I think the terms of this sequence can be determined in logarithmic time. Any help will be highly appreciated.

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Solution

A closed form of the sequence is

a(n) = (n*Luc(n+6) - 4*Fib(n))/5

where Luc(k) is the k-th Lucas number, and Fib(k) the k-th Fibonacci number. Since Luc(k) = Fib(k+1) + Fib(k-1), the formula can easily be rewritten to use only Fibonacci numbers.

OTHER TIPS

Can you provide more members of the sequence?

Nvm, I got it.

a[n] = a[n-1] + a[n-2] + Fibonacci[n+5]

Searching for part of sequence 5,18,44 on OEIS, gives A037140. That sequence is of form:

a(n) = F(n+9)-(29+8*n)

Trying similar approach with parts of Fibonacci sequence on F(n+k)-your_sequence(n) gives:

F(n+10)-your_sequence(n) = 50, 71, 100, 137, 182

That sequence has nice progression: 29+21*n+8*n*(n-1)/2. This sequence has presentation:

a(n) = F(n+10)-(29+21*n+4*n*(n-1)), n=0, 1, ...
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