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 A097823 #9 Feb 16 2025 08:32:54 %S A097823 40,603,798,890,917,1245,1253,1318,1640,1651,1721,2010,2069,2251,2452, %T A097823 2606,2649,3094,3099,3321,3402,3527,3607,4123,4239,4301,4819,4943, %U A097823 5002,5083,5308,5372,5425,5736,5790,5930,5958,5998,6150,6416,6511,6683,6764 %N A097823 Numbers n such that n^2+n+41 (Euler's "prime generating polynomial") is not squarefree. %H A097823 Harvey P. Dale, <a href="/A097823/b097823.txt">Table of n, a(n) for n = 1..1000</a> %H A097823 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Prime-GeneratingPolynomial.html">Prime-Generating Polynomial</a> %e A097823 a(1)=40: p(40)=40^2+40+41=1681=41^2, a(2)=603: p(603)=364253=197*43^2, a(11)=1721: p(1721)=2963603=43*41^3, a(68)=10428: p(10428)=108753653=743^2*197, a(91)=14144: p(14144)=200066921=47^4*41. %t A097823 Select[Range[10000],!SquareFreeQ[#^2+#+41]&] (* _Harvey P. Dale_, Nov 06 2011 *) %Y A097823 Cf. A013929 n is not squarefree, A002837 n such that n^2-n+41 is prime, A007634 n such that n^2+n+41 is composite, A005846 primes of form n^2+n+41, A097822 n^2+n+41 has more than 2 prime factors. %K A097823 nonn %O A097823 1,1 %A A097823 _Hugo Pfoertner_, Aug 26 2004