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 A134020 #24 Jul 28 2023 18:58:57
%S A134020 8,15,35,143,323,899,1763,3599,5183,10403,11663,19043,22499,32399,
%T A134020 36863,39203,51983,57599,72899,79523,97343,121103,176399,186623,
%U A134020 213443,272483,324899,359999,381923,412163,435599,656099,675683,685583,736163
%N A134020 Numbers that are one less than a square and have exactly 4 divisors.
%C A134020 A037074 is a subsequence. - _R. J. Mathar_, Jun 08 2008
%H A134020 Vincenzo Librandi, <a href="/A134020/b134020.txt">Table of n, a(n) for n = 1..5400</a>
%p A134020 with(numtheory): a:=proc(n) if type(sqrt(n+1),integer)=true and tau(n)=4 then n else end if end proc: seq(a(n),n=1..800000); # _Emeric Deutsch_, Jan 27 2008
%t A134020 t={}; Do[If[DivisorSigma[0,n]==4&&IntegerQ[Sqrt[n+1]],AppendTo[t,n]],{n,10^6}]; t (* _Jayanta Basu_, Jun 03 2013 *)
%t A134020 Select[Range[1000]^2-1,DivisorSigma[0,#]==4&] (* _Harvey P. Dale_, Jul 28 2023 *)
%K A134020 nonn
%O A134020 1,1
%A A134020 _Giovanni Teofilatto_, Jan 11 2008
%E A134020 Edited and extended by _Emeric Deutsch_, Jan 27 2008
%E A134020 Name reworded by _Jon E. Schoenfield_, Jan 15 2019