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 A154378 #23 Sep 16 2016 02:42:11
%S A154378 240,490,740,990,1240,1490,1740,1990,2240,2490,2740,2990,3240,3490,
%T A154378 3740,3990,4240,4490,4740,4990,5240,5490,5740,5990,6240,6490,6740,
%U A154378 6990,7240,7490,7740,7990,8240,8490,8740,8990,9240,9490,9740,9990,10240,10490
%N A154378 a(n) = 250*n - 10.
%C A154378 The identity (1250*n^2 - 100*n + 1)^2 - (25*n^2 - 2*n)*(250*n - 10)^2 = 1 can be written as A154374(n)^2 - A154376(n)*a(n)^2 = 1 (see also the second comment in A154374). - _Vincenzo Librandi_, Jan 30 2012
%H A154378 Vincenzo Librandi, <a href="/A154378/b154378.txt">Table of n, a(n) for n = 1..10000</a>
%H A154378 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F A154378 a(n) = 2*a(n-1) - a(n-2). - _Vincenzo Librandi_, Jan 30 2012
%F A154378 G.f.: 10*x*(x + 24)/(1-x)^2. - _Vincenzo Librandi_, Jan 30 2012
%F A154378 E.g.f.: 10*( (25*x - 1)*exp(x) + 1). - _G. C. Greubel_, Sep 15 2016
%t A154378 LinearRecurrence[{2, -1}, {240, 490}, 50] (* _Vincenzo Librandi_, Jan 30 2012 *)
%o A154378 (PARI) a(n)=250*n-10 \\ _Charles R Greathouse IV_, Dec 27 2011
%Y A154378 Cf. A154374, A154376.
%K A154378 nonn,easy
%O A154378 1,1
%A A154378 _Vincenzo Librandi_, Jan 08 2009