A171709 - OEIS

%I #14 Sep 08 2022 08:45:50

%S 0,-5,-8,-1,-8,-5,0,7,16,1,40,55,8,91,112,5,160,187,8,247,280,35,352,

%T 391,16,475,520,7,616,667,80,775,832,11,952,1015,40,1147,1216,143,

%U 1360,1435,56,1591,1672,65,1840,1927,224,2107,2200,85,2392,2491,32,2695,2800,323,3016,3127,40,3355,3472,133,3712

%N Numerator of 1/9 - 1/n^2.

%C A061039 extended to negative n. a(0)=-1 is defined at the pole where the expression is undefined.

%H G. C. Greubel, <a href="/A171709/b171709.txt">Table of n, a(n) for n = -3..1000</a>

%F a(n) = A061039(n), n>2.

%F a(n) = a(-n).

%p seq( `if`(n=0, -1, numer(1/9 -1/n^2)), n=-3..65); # _G. C. Greubel_, Nov 29 2019

%t Table[If[n==0, -1, Numerator[1/9 -1/n^2]], {n, -3, 65}] (* _G. C. Greubel_, Nov 29 2019 *)

%o (PARI) a(n) = if(n==0, -1, numerator(1/9 -1/n^2)); \\ _G. C. Greubel_, Nov 29 2019

%o (Magma) [n eq 0 select -1 else Numerator(1/9 -1/n^2): n in [-3..65]]; // _G. C. Greubel_, Nov 29 2019

%o (Sage)

%o def a(n):

%o     if (n==0): return -1

%o     else: return numerator(1/9 -1/n^2)

%o [a(n) for n in (-3..65)] # _G. C. Greubel_, Nov 29 2019

%Y Cf. A067998.

%K sign,easy,frac

%O -3,2

%A _Paul Curtz_, Dec 16 2009

%E Offset set to -3 by _R. J. Mathar_, Nov 23 2010