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 A201123 #13 Feb 21 2025 14:52:45
%S A201123 3,19,166,894,5703,12654,620046,4235622,24518766,133763479,575536407,
%T A201123 7275224659,63521178243,36407018199,1783943891751,12048048160062,
%U A201123 62797942092807,615169213046419,4293026969512678,29406470217788179,174254081653289398,2627356192258967382
%N A201123 Differences between odd powers of 7 and the next smaller square.
%H A201123 Hugo Pfoertner, <a href="/A201123/b201123.txt">Table of n, a(n) for n = 1..500</a>
%F A201123 a(n) = 7^(2*n-1) - floor(sqrt(7^(2*n-1)))^2.
%e A201123 a(1) = 7^1 - 2^2 = 3;
%e A201123 a(2) = 7^3 - 18^2 = 343 - 324 = 19;
%e A201123 a(3) = 7^5 - 129^2 = 16807 - 16641 = 166.
%t A201123 Table[7^(2 n - 1) - Floor[Sqrt[7^(2 n - 1)]]^2, {n, 30}] (* _Wesley Ivan Hurt_, Mar 06 2014 *)
%Y A201123 Cf. A051218.
%K A201123 nonn
%O A201123 1,1
%A A201123 _Hugo Pfoertner_, Nov 27 2011