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 A026440 #18 Feb 06 2025 13:51:20
%S A026440 1,4,5,6,7,8,9,10,11,12,13,14,16,17,18,20,21,22,25,26,28,30,32,33,36,
%T A026440 37,38,40,42,45,46,50,52,56,57,58,60,61,66,68,70,72,73,74,75,78,81,82,
%U A026440 85,86,88,91,92,93,94,96,100,102,105,106
%N A026440 a(n) = least positive integer > a(n-1) and not a(i)*a(j)-1 for 1 <= i <= j < n, n >= 2, with initial terms 1,4.
%H A026440 Ivan Neretin, <a href="/A026440/b026440.txt">Table of n, a(n) for n = 1..1000</a>
%t A026440 a = {1, 4}; used = Flatten@Outer[Times, a, a] - 1; Do[k = a[[-1]] + 1; While[MemberQ[used, k], k++]; AppendTo[a, k]; used = Union[used, k*a - 1], {n, 3, 60}]; a (* _Ivan Neretin_, Feb 15 2018 *)
%Y A026440 Cf. A026437 and references therein.
%K A026440 nonn
%O A026440 1,2
%A A026440 _Clark Kimberling_
%E A026440 Name clarified by _Robert C. Lyons_, Feb 06 2025