A226787 If n=0 (mod 3) then a(n)=0, otherwise a(n)=9^(-1) in Z/nZ*.

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, 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, 46, 0, 34, 7, 0, 57, 29

Offset: 1

Author

José María Grau Ribas, Jun 18 2013

Keywords

• nonn
• easy

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A092092, A226782-A226786.

Programs

Mathematica

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}]
(* Second program: *)
Table[If[Mod[n, 3] == 0, 0, ModularInverse[9, n], 0], {n, 1, 100}] (* Jean-François Alcover, Mar 14 2023 *)

PARI

a(n)=if(n%3,lift(Mod(1,n)/9),0) \\ Charles R Greathouse IV, Jun 18 2013

Formula

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