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 A171669 #9 Aug 08 2024 06:44:22
%S A171669 12,5741,2744210,15994428,21300003689580,723573111879672,
%T A171669 1111984844349868137938112,293199986221627877463941823267862,
%U A171669 9960168529794442859224531878561050,27749033099085295754434173207717704165,66992092050551637663438906713182313772
%N A171669 Pell numbers sandwiched between two numbers having same number of divisors.
%H A171669 Amiram Eldar, <a href="/A171669/b171669.txt">Table of n, a(n) for n = 1..19</a>
%t A171669 f[n_]:=Length[Divisors[n]]; a=1;b=0;c=0;lst={};Do[c=a+b+c;If[f[c-1]==f[c+1],AppendTo[lst,c]];a=b;b=c,{n,80}];lst
%Y A171669 Cf. A000005, A000129, A005237, A005238, A067889, A171666, A171667, A171668.
%K A171669 nonn
%O A171669 1,1
%A A171669 _Vladimir Joseph Stephan Orlovsky_, Dec 14 2009
%E A171669 a(8)-a(11) from _Amiram Eldar_, Aug 08 2024