%I
%S 3,5,6,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,
%T 29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,
%U 52,53,54,55,56,57,58,59,60,61,62,63,64,65
%N Number of segments needed to draw the spiral of equilateral triangles with side lengths which follow the Padovan sequence.
%D Mohammad K. Azarian, A Trigonometric Characterization of Equilateral Triangle, Problem 336, Mathematics and Computer Education, Vol. 31, No. 1, Winter 1997, p. 96. Solution published in Vol. 32, No. 1, Winter 1998, pp. 8485.
%D Mohammad K. Azarian, Equating Distances and Altitude in an Equilateral Triangle, Problem 316, Mathematics and Computer Education, Vol. 28, No. 3, Fall 1994, p. 337. Solution published in Vol. 29, No. 3, Fall 1995, pp. 324325.
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,1).
%F a(1)=3: a(2)=5: a(3)=6; for n>3, a(n)=n+4.
%t LinearRecurrence[{2,1},{3,5,6,8,9},70] (* _Harvey P. Dale_, Dec 21 2018 *)
%o (PARI) a(n)=if(n>3,n+4,[3,5,6][n]) \\ _Charles R Greathouse IV_, Oct 27 2011
%Y Cf. Padovan sequence: A000931.
%K easy,nonn
%O 1,1
%A _Omar E. Pol_, Nov 04 2007, Nov 05 2007
