%I #20 Mar 14 2023 11:41:40

%S 0,1,0,1,4,0,4,1,0,9,5,0,3,11,0,9,2,0,17,9,0,5,18,0,14,3,0,25,13,0,7,

%T 25,0,19,4,0,33,17,0,9,32,0,24,5,0,41,21,0,11,39,0,29,6,0,49,25,0,13,

%U 46,0,34,7,0,57,29

%N If n=0 (mod 3) then a(n)=0, otherwise a(n)=9^(-1) in Z/nZ*.

%H Charles R Greathouse IV, <a href="/A226787/b226787.txt">Table of n, a(n) for n = 1..10000</a>

%F Empirical g.f.: -x^2*(x^17-x^14-3*x^12-x^11-3*x^9-9*x^8-x^6-4*x^5-4*x^3-x^2-1) / (x^18 -2*x^9 +1). - _Colin Barker_, Jun 20 2013

%t Inv[a_, mod_] := Which[mod == 1,0, GCD[a, mod] > 1, 0, True, Last@Reduce[a*x == 1, x, Modulus -> mod]];Table[Inv[9, n], {n, 1, 122}]

%t (* Second program: *)

%t Table[If[Mod[n, 3] == 0, 0, ModularInverse[9, n], 0], {n, 1, 100}] (* _Jean-François Alcover_, Mar 14 2023 *)

%o (PARI) a(n)=if(n%3,lift(Mod(1,n)/9),0) \\ _Charles R Greathouse IV_, Jun 18 2013

%Y Cf. A092092, A226782-A226786.

%K nonn,easy

%O 1,5

%A _José María Grau Ribas_, Jun 18 2013