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 A173294 #10 Jan 16 2019 14:59:11
%S A173294 7,7,47,47,119,119,223,223,359,359,527,527,727,727,959,959,1223,1223,
%T A173294 1519,1519,1847,1847,2207,2207,2599,2599,3023,3023,3479,3479,3967,
%U A173294 3967,4487,4487,5039,5039,5623,5623,6239,6239,6887,6887,7567,7567,8279,8279,9023,9023,9799,9799,10607,10607,11447,11447,12319,12319,13223,13223,14159,14159,15127,15127,16127
%N A173294 Values of 16*n^2+24*n+7, n>=0, each duplicated.
%C A173294 The Leibniz series for Pi/4 involves 1, -1/3, 1/5, -1/7, 1/9, -1/11, .. inverses of the odd numbers. The first differences of this sequence of fractions are -4/3, 8/15, -12/35, 16/63, -20/99, 24/143,... = (-1)^(n+1)*A008586(n+1)/A000466(n+1).
%C A173294 a(n) is the difference of the n-th denominator and numerator, A000466(n+1)+(-1)^n*A008586(n+1). (Note that A000466 is a bisection of A005563, which establishes a very distant relation between this sequence and the Lyman series.)
%C A173294 If one would add the n-th denominator and numerator, -1, 23, 23, 79, 79, 167, 167, 287, 287, 439,...(duplicated values of 16n^2+40n+23 and a -1) would result.
%H A173294 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,2,-2,-1,1).
%F A173294 a(n) = +a(n-1) +2*a(n-2) -2*a(n-3) -a(n-4) +a(n-5).
%F A173294 G..f: ( -7-26*x^2+x^4 ) / ( (1+x)^2*(x-1)^3 ).
%F A173294 a(2n) = a(2n+1) = 16n^2+24n+7.
%t A173294 With[{c=16n^2+24n+7},Table[{c,c},{n,0,40}]]//Flatten (* or *) LinearRecurrence[ {1,2,-2,-1,1},{7,7,47,47,119},80] (* _Harvey P. Dale_, Jan 16 2019 *)
%K A173294 nonn,easy
%O A173294 0,1
%A A173294 _Paul Curtz_, Feb 15 2010