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A072703
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Indices of Fibonacci numbers whose last digit is 5.
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2
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5, 10, 20, 25, 35, 40, 50, 55, 65, 70, 80, 85, 95, 100, 110, 115, 125, 130, 140, 145, 155, 160, 170, 175, 185, 190, 200, 205, 215, 220, 230, 235, 245, 250, 260, 265, 275, 280, 290, 295, 305, 310, 320, 325, 335, 340, 350, 355, 365, 370, 380
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OFFSET
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1,1
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COMMENTS
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Sequence contains numbers of the forms 5 + 60*k, 10 + 60*k, 20 + 60*k, 25 + 60*k, 35 + 60*k, 40 + 60*k, 50 + 60*k, 55 + 60*k, where k>=0.
Numbers that are congruent to {5, 10, 20, 25} mod 30. - Amiram Eldar, Jan 01 2022
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LINKS
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FORMULA
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a(1)=5, a(2)=10, a(3)=20, a(n)=a(n-1)+a(n-2)-a(n-3). - Harvey P. Dale, May 15 2011
G.f.: 5*x*(x^2+x+1) / ((x-1)^2*(x+1)). - Colin Barker, Jun 16 2013
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MATHEMATICA
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Flatten[Position[Fibonacci[Range[400]], _?(Last[IntegerDigits[#]]==5&)]] (* or *) LinearRecurrence[{1, 1, -1}, {5, 10, 20}, 60] (* or *) Table[-(5/4) (3+(-1)^n-6 n), {n, 60}] (* Harvey P. Dale, May 15 2011 *)
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CROSSREFS
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KEYWORD
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nonn,base,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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