OFFSET
2,1
COMMENTS
Sequence may be obtained by starting with the segment (9, 37) followed by the line from 37 in the direction 37, 81,... in the square spiral whose vertices are the generalized hexagonal numbers (A000217). - Omar E. Pol, Jun 26 2016
LINKS
Colin Barker, Table of n, a(n) for n = 2..1000
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
From Colin Barker, May 18 2016: (Start)
a(n) = 3*a(n-1)-3*a(n-2)+a(n-3) for n>4.
G.f.: x^2*(9+10*x-3*x^2) / (1-x)^3.
(End)
MATHEMATICA
Table[8 n^2 - 12 n + 1, {n, 2, 45}] (* or *)
Drop[#, 2] &@ CoefficientList[Series[x^2 (9 + 10 x - 3 x^2)/(1 - x)^3, {x, 0, 45}], x] (* Michael De Vlieger, Jun 26 2016 *)
PROG
(PARI) Vec(x^2*(9+10*x-3*x^2)/(1-x)^3 + O(x^50)) \\ Colin Barker, May 18 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Dimitri Boscainos, May 18 2016
STATUS
approved