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A202338
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Smallest Fibonacci number which when appended to n produces a prime number.
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1
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1, 3, 1, 1, 3, 1, 1, 3, 377, 1, 3, 13, 1, 89, 1, 3, 3, 1, 1, 89, 1, 3, 3, 1, 1, 3, 1, 1, 3, 89, 1, 21, 1, 13, 3, 13, 3, 3, 89, 1, 233, 1, 1, 3, 13, 1, 21, 13, 1, 3, 13, 1, 233, 1, 21, 3, 1, 13, 3, 1, 3, 21, 1, 1, 3, 1, 3, 3, 1, 1, 21, 13, 3, 3, 1, 1, 3, 233
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OFFSET
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1,2
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LINKS
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EXAMPLE
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a(9) = 377 because 9 concatenated with 377 gives the prime 9377.
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MAPLE
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with(combinat, fibonacci):for n from 1 to 80 do: i:=0:for m from 1 to 2000 while(i=0) do:p:=fibonacci(m): nn:=length(p): x:=n*10^nn+p: if type(x, prime)=true then i:=1: printf(`%d, `, p):else fi:od:od:
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MATHEMATICA
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f[n_]:=Block[{p=1, a=IntegerDigits[n]}, While[!PrimeQ[FromDigits[Join[a, IntegerDigits[Fibonacci[p]]]]], p++]; Fibonacci[p]]; Table[f[n], {n, 92}]
With[{fibs=Fibonacci[Range[20]], nn=80}, Table[SelectFirst[fibs, PrimeQ[ n*10^ IntegerLength[ #]+ #]&], {n, nn}]] (* Harvey P. Dale, Feb 28 2020 *)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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