A276811 a(n) = sigma(Fibonacci(k))/Fibonacci(n) where k is the least number such that Fibonacci(n) divides sigma(Fibonacci(k)), or -1 if no such k exists.
1, 1, 2, 1, 3, 4, 31, 20, 47, 5832, 322, 84, 4576568315415066934826490, 324, 843, 480, 3769607182320, 2209, 707932145558030519866865515025923563263974776037874477588352, 69670959389872974262939756520, 39603
Offset: 1
Keywords
Examples
a(7) = 31 because least k such that Fibonacci(7) divides sigma(Fibonacci(k)) is 12 and sigma(Fibonacci(12))/Fibonacci(7) = 31.
Programs
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Mathematica
f[n_] := Block[{k = 1, fn = Fibonacci@ n}, While[ds = DivisorSigma[1, Fibonacci[k]]; Mod[ds, fn] > 0, k++]; ds/fn]; Array[f, 21] (* Robert G. Wilson v, Nov 06 2016 *)
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