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 A134420 #17 Feb 22 2021 03:41:47
%S A134420 10,26,65,82,122,145,170,226,290,362,442,485,530,626,730,785,842,901,
%T A134420 962,1090,1157,1226,1370,1522,1765,1937,2026,2117,2210,2305,2402,2501,
%U A134420 2602,2705,2810,3026,3365,3482,3601,3722,3845,3970,4097,4226,4490,4762
%N A134420 Composite squarefree numbers of the form k^2 + 1.
%C A134420 Square roots of these numbers are quadratic irrationals and corresponding chain fraction representations are periodic: sqrt(10) = [3;{2,3}], sqrt(26) = [5;{2,5}], sqrt(65) = [8;{2,8}], ..., where {} is denoted a period (we write {6} == {2,3}).
%H A134420 Amiram Eldar, <a href="/A134420/b134420.txt">Table of n, a(n) for n = 1..10000</a>
%F A134420 a(n) = A002522(A134427(n)). - _Amiram Eldar_, Feb 22 2021
%e A134420 a(1)=10 because 10 = 3^2 + 1 is squarefree.
%e A134420 a(2)=26 because 26 = 5^2 + 1 is squarefree.
%e A134420 a(3)=65 because 65 = 8^2 + 1 is squarefree.
%p A134420 ts_fn3:=proc(n) local i,tren,ans; ans:=[ ]: for i from 1 to n do tren := i^(2)+1: if (isprime(tren) = false and numtheory[mobius] (tren) <> 0 ) then ans:=[ op(ans), tren ]: fi od: RETURN(ans) end: ts_fn3(200);
%t A134420 Select[Range[70]^2+1, CompositeQ[#] && SquareFreeQ[#] &] (* _Amiram Eldar_, Feb 22 2021 *)
%Y A134420 Cf. A002496, A002522, A124809, A134427.
%K A134420 nonn
%O A134420 1,1
%A A134420 _Jani Melik_, Jan 18 2008
%E A134420 Definition corrected by _T. D. Noe_, Sep 16 2008