OFFSET
1,2
COMMENTS
Also nonnegative integers x in the solutions to 2*x^2-6*y^2+4*x+4*y+2+2 = 0, the corresponding values of y being A046184.
LINKS
Colin Barker, Table of n, a(n) for n = 1..874
Index entries for linear recurrences with constant coefficients, signature (15,-15,1).
FORMULA
a(n) = 15*a(n-1)-15*a(n-2)+a(n-3).
G.f.: 2*x^2*(x-7) / ((x-1)*(x^2-14*x+1)).
a(n) = (-6-(7-4*sqrt(3))^n*(3+2*sqrt(3))+(-3+2*sqrt(3))*(7+4*sqrt(3))^n)/6. - Colin Barker, Mar 05 2016
a(n) = 14*a(n-1) - a(n-2) + 12. - Vincenzo Librandi, Mar 05 2016
EXAMPLE
14 is in the sequence because T(14)+T(15) = 105+120 = 225 = N(9).
MATHEMATICA
RecurrenceTable[{a[1] == 0, a[2] == 14, a[n] == 14 a[n-1]- a[n-2] + 12}, a, {n, 20}] (* Vincenzo Librandi, Mar 05 2016 *)
PROG
(PARI) concat(0, Vec(2*x^2*(x-7) / ((x-1)*(x^2-14*x+1)) + O(x^100)))
(Magma) I:=[0, 14]; [n le 2 select I[n] else 14*Self(n-1)-Self(n-2)+12: n in [1..20]]; // Vincenzo Librandi, Mar 05 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Dec 11 2014
STATUS
approved