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 A306666 #15 Nov 25 2019 01:06:35 %S A306666 1,2,3,7,21 %N A306666 Positive integers x such that x*(7-5*x+x^2)*(6-4*x+x^2) is a square. %C A306666 No other terms below 10^6. %C A306666 No other terms below 10^10. - _Chai Wah Wu_, Nov 24 2019 %H A306666 dxdy forum, <a href="https://dxdy.ru/post1379764.html">x(7-5x+x^2)(6-4x+x^2)=y^2 in natural numbers</a> (in Russian). %t A306666 Select[Range[1000], IntegerQ[Sqrt[#*(7 - 5*# + #^2)*(6 - 4*# + #^2)]] &] (* _Vaclav Kotesovec_, Mar 10 2019 *) %o A306666 (PARI) isok(x)=issquare(x*(7-5*x+x^2)*(6-4*x+x^2)); %o A306666 (Python) %o A306666 from sympy.ntheory.primetest import is_square %o A306666 A306666_list = [n for n in range(1,10**3) if is_square(n*(n*(n*(n*(n - 9) + 33) - 58) + 42))] # _Chai Wah Wu_, Nov 24 2019 %K A306666 nonn,more %O A306666 1,2 %A A306666 _Dmitry Ezhov_, Mar 04 2019