This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A174680 #20 Sep 26 2018 21:43:29
%S A174680 -1,-15,-3,-7,0,9,5,33,3,65,21,105,1,153,45,209,15,273,77,345,3,425,
%T A174680 117,513,35,609,165,713,3,825,221,945,63,1073,285,1209,5,1353,357,
%U A174680 1505,99,1665,437,1833,15,2009,525,2193,143,2385,621,2585,21,2793,725,3009,195,3233,837,3465,14,3705
%N A174680 Numerator of 1/16 - 1/n^2, using -1 at the pole where n=0.
%C A174680 Extends the Brackett spectrum to negative principal quantum numbers in the spirit of A144477 and A171709.
%H A174680 G. C. Greubel, <a href="/A174680/b174680.txt">Table of n, a(n) for n = 0..10000</a>
%F A174680 a(n) = A061041(n), n >= 4.
%F A174680 a(n) = A172157(4,n), n >= 1.
%F A174680 a(n) = a(-n) for all n in Z.
%t A174680 Table[(n^2 - 16)/(GCD[n^2 - 16, 16*n^2]), {n, 0, 100}] (* _G. C. Greubel_, Sep 16 2018 *)
%o A174680 (PARI) {a(n) = (n^2 - 16) / gcd(n^2 - 16, 16 * n^2)}; /* _Michael Somos_, Jan 06 2011 */
%Y A174680 Cf. A174233, A067998.
%K A174680 sign,easy
%O A174680 0,2
%A A174680 _Paul Curtz_, Nov 30 2010
%E A174680 removed a(-4)-a(-1) since a(-n)=a(n) by _Michael Somos_, Jan 06 2011