OFFSET
1,1
COMMENTS
Numbers n such that n == 27 or 46 (mod 73).
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (1,1,-1).
FORMULA
G.f.: x*(27 + 19*x + 27*x^2)/((1 + x)*(1 - x)^2).
a(n) = a(n-1) + a(n-2) - a(n-3) for n>2.
a(n) = a(n-2) + 73 for all n>2.
a(n) = -27*(-1)^n + 73*floor(n/2).
MATHEMATICA
Select[Range[1500], PowerMod[#, 2, 73] == 72 &] (* or *) CoefficientList[ Series[(27 + 19 x + 27 x^2)/((1 + x) (1 - x)^2), {x, 0, 100}], x]
Table[73n+{27, 46}, {n, 0, 30}]//Flatten (* or *) LinearRecurrence[{1, 1, -1}, {27, 46, 100}, 60] (* Harvey P. Dale, Jun 13 2017 *)
PROG
(Magma) I:=[27, 46, 100]; [n le 3 select I[n] else Self(n-1)+Self(n-2)-Self(n-3): n in [1..50]];
(Magma) [-27*(-1)^n+73*Floor(n/2): n in [1..50]];
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Apr 25 2014
STATUS
approved