A070440 - OEIS

%I #24 Apr 06 2016 18:04:22

%S 0,1,4,9,16,7,0,13,10,9,10,13,0,7,16,9,4,1,0,1,4,9,16,7,0,13,10,9,10,

%T 13,0,7,16,9,4,1,0,1,4,9,16,7,0,13,10,9,10,13,0,7,16,9,4,1,0,1,4,9,16,

%U 7,0,13,10,9,10,13,0,7,16,9,4,1,0,1,4,9,16,7,0,13,10,9,10,13,0,7,16,9

%N a(n) = n^2 mod 18.

%H G. C. Greubel, <a href="/A070440/b070440.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_18">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1).

%F a(n) = a(n-18). - _R. J. Mathar_, Jul 27 2015

%F G.f.: -x*(1 +4*x +9*x^2 +16*x^3 +7*x^4 +13*x^6 +10*x^7 +9*x^8 +10*x^9 +13*x^10 +7*x^12 +16*x^13 +9*x^14 +4*x^15 +x^16) / ( (x-1)*(1+x+x^2)*(1+x^3+x^6)*(1+x)*(1-x+x^2)*(1-x^3+x^6) ). - _R. J. Mathar_, Jul 27 2015

%t Table[Mod[n^2,18],{n,0,200}] (* _Vladimir Joseph Stephan Orlovsky_, Apr 23 2011 *)

%o (PARI) a(n)=n^2%18 \\ _Charles R Greathouse IV_, Apr 06 2016

%Y Cf. A070441, A070442.

%K nonn,easy

%O 0,3

%A _N. J. A. Sloane_, May 12 2002