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a(n) = n^2 mod 26.
2

%I #23 Dec 18 2023 13:51:36

%S 0,1,4,9,16,25,10,23,12,3,22,17,14,13,14,17,22,3,12,23,10,25,16,9,4,1,

%T 0,1,4,9,16,25,10,23,12,3,22,17,14,13,14,17,22,3,12,23,10,25,16,9,4,1,

%U 0,1,4,9,16,25,10,23,12,3,22,17,14,13,14,17,22,3,12,23,10,25,16,9,4,1

%N a(n) = n^2 mod 26.

%H G. C. Greubel, <a href="/A070448/b070448.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_26">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, 0, 0, 0, 0, 0, 0, 0, 0, 1).

%F G.f.: (x +4*x^2 +9*x^3 +16*x^4 +25*x^5 +10*x^6 +23*x^7 +12*x^8 +3*x^9 +22*x^10 +17*x^11 +14*x^12 +13*x^13 +14*x^14 +17*x^15 + 22*x^16 + 3*x^17 +12*x^18 +23*x^19 +10*x^20 +25*x^21 +16*x^22 +9*x^23 +4*x^24 +x^25)/(1-x^26). - _Vincenzo Librandi_, Dec 16 2014

%F a(n) = a(n-26). - _G. C. Greubel_, Mar 24 2016

%p A070448:=n->n^2 mod 26: seq(A070448(n), n=0..150); # _Wesley Ivan Hurt_, Apr 09 2017

%t Table[Mod[n^2,26],{n,0,200}] (* _Vladimir Joseph Stephan Orlovsky_, Apr 23 2011 *)

%t PowerMod[Range[0,80],2,26] (* _Harvey P. Dale_, Dec 15 2014 *)

%o (PARI) a(n)=n^2%26 \\ _Charles R Greathouse IV_, Apr 06 2016

%K nonn,easy

%O 0,3

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