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 A331802 #17 Feb 25 2020 02:11:47 %S A331802 1,2,3,4,5,6,7,9,10,11,14,15,19,23 %N A331802 Integers having no representation as sum of two nonsquarefree numbers. %C A331802 This sequence is finite with 14 terms and 23 is the largest term (see Prime Curios link); a proof can be found in comments of A331801. %H A331802 G. L. Honaker, Jr. and Chris K. Caldwell, <a href="https://primes.utm.edu/curios/page.php?curio_id=5071">Prime Curios! 23</a> %e A331802 With the two smallest nonsquarefree numbers 4 and 8, it is not possible to get 1, 2, 3, 4, 5, 6, 7, 9, 10 and 11 as sum of two nonsquarefree numbers. %t A331802 max = 25; Complement[Range[max], Union @ Select[Total /@ Tuples[Select[Range[max], !SquareFreeQ[#] &], 2], # <= max &]] (* _Amiram Eldar_, Feb 24 2020 *) %Y A331802 Cf. A005117 (squarefree), A013929 (nonsquarefree), A331801 (complement). %Y A331802 Cf. A000404 (sum of 2 nonzero squares), A018825 (not the sum of 2 nonzero squares). %Y A331802 Cf. A001694 (squareful), A052485 (not squareful), A076871 (sum of 2 squareful), A085253 (not the sum of 2 squareful). %K A331802 nonn,full,fini %O A331802 1,2 %A A331802 _Bernard Schott_, Feb 23 2020