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A121927
Minimum k>0 such that Sum_{i=1..n} Fibonacci(i)*k^(i-1) is prime.
0
1, 2, 1, 6, 10, 39, 6, 44, 165, 2, 8, 23, 50, 18, 30, 1634, 232, 80, 1070, 6, 16, 48, 108, 3, 244, 5254, 232, 49910, 15946, 270, 240, 92, 15, 14, 308, 60, 4, 31980, 2460, 224, 646, 226, 626, 144, 3, 1932, 3528, 766, 6424, 36
OFFSET
2,2
COMMENTS
Let f(k,n) = Sum_{i=1..n} Fibonacci(i)*k^(i-1) where Fibonacci(i) = A000045(i). Corresponding smallest primes of the form f(k,n) or f(a(n),n) are {2,11,7,7207,853211,46477210729,6554599,484440107670157,...}.
EXAMPLE
a(2) = 1 because f(1,2) = 1*1 + 1 = 2 is prime.
a(3) = 2 because f(2,3) = 2*2^2 + 1*2 + 1 = 11 is prime but f(1,3) = 2*1^2 + 1*1 + 1 = 4 is not prime.
a(4) = 1 because f(1,4) = 3*1^3 + 2*1^2 + 1*1 + 1 = 7 is prime.
CROSSREFS
Cf. A000045.
Sequence in context: A069114 A173773 A305512 * A200265 A039762 A039795
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Sep 02 2006
STATUS
approved