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A072703 Indices of Fibonacci numbers whose last digit is 5. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..51.

Index entries for linear recurrences with constant coefficients, signature (1,1,-1).

FORMULA

Sequence contains numbers of the forms 5+60k, 10+60k, 20+60k, 25+60k, 35+60k, 40+60k, 50+60k, 55+60k, where k>=0.

a(n)=15*(n-1)-a(n-1), with a(1)=5. - Vincenzo Librandi, Aug 08 2010]

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

a(n)=-(5/4)*(3+(-1)^n-6*n). - Harvey P. Dale, May 15 2011

G.f.: 5*x*(x^2+x+1) / ((x-1)^2*(x+1)). - Colin Barker, Jun 16 2013

EXAMPLE

a(2)=15*1-5=10; a(3)=15*2-10=20; a(4)=15*3-20=25; a(5)=15*4-25=35. - Vincenzo Librandi, Aug 08 2010

MATHEMATICA

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 *)

CROSSREFS

Cf. A000045, A003893.

Sequence in context: A062052 A245387 A115799 * A086761 A045191 A065958

Adjacent sequences:  A072700 A072701 A072702 * A072704 A072705 A072706

KEYWORD

nonn,base,easy

AUTHOR

Benoit Cloitre, Aug 07 2002

EXTENSIONS

Edited by M. F. Hasler, Oct 08 2014

STATUS

approved

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Last modified June 28 04:43 EDT 2017. Contains 288813 sequences.