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%I #39 Mar 12 2024 02:40:07
%S 1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,
%T 5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,
%U 1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6,1,2,5,6
%N Period 4: repeat [1, 2, 5, 6].
%C Decimal expansion of 1256/9999. - _Klaus Brockhaus_, May 20 2010
%H Salvatore Gambino, <a href="http://digilander.libero.it/salgam">Terne pitagoriche primitive</a> (in Italian).
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,1).
%F a(n) = (7 + (-1)^n + 4*(-1)^(2*n + 1 - (-1)^n)/4)/2.
%F G.f.: (1 + 2*x + 5*x^2 + 6*x^3)/((1-x)*(x+1)*(x^2+1)). - _R. J. Mathar_, Jan 13 2008
%F a(n) = A000111(n+2) mod 10.
%F a(n) = 7/2 - 2*cos(Pi*n/2) - 2*sin(Pi*n/2) - (-1)^n/2. - _R. J. Mathar_, Oct 08 2011
%F a(n) = a(n-4) for n>3. - _Wesley Ivan Hurt_, Jul 10 2016
%p seq(op([1, 2, 5, 6]), n=0..50); # _Wesley Ivan Hurt_, Jul 10 2016
%t PadRight[{}, 100, {1, 2, 5, 6}] (* _Wesley Ivan Hurt_, Jul 10 2016 *)
%o (PARI) a(n)=[1,2,5,6][n%4+1] \\ _Charles R Greathouse IV_, Oct 07 2015
%o (Magma) &cat [[1, 2, 5, 6]^^30]; // _Wesley Ivan Hurt_, Jul 10 2016
%o (Python)
%o def A131800(n): return (1,2,5,6)[n&3] # _Chai Wah Wu_, Apr 18 2023
%Y Cf. A000111, A178131 (decimal expansion of (11+3*sqrt(21))/17).
%K nonn,easy
%O 0,2
%A Salvatore Gambino (salvatore.gambino(AT)fastwebnet.it), Oct 04 2007
%E More terms from _R. J. Mathar_, Jan 13 2008
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