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 A026438 #17 Feb 06 2025 13:51:28
%S A026438 1,3,4,5,6,7,9,10,12,13,16,18,21,22,25,28,30,31,32,33,36,37,40,42,43,
%T A026438 45,46,50,52,54,55,56,57,58,60,61,66,67,68,70,72,73,75,76,78,81,82,84,
%U A026438 85,86,88,91,93,94,96,97,100,101,102,103
%N A026438 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 1,3.
%H A026438 Ivan Neretin, <a href="/A026438/b026438.txt">Table of n, a(n) for n = 1..1000</a>
%t A026438 a = {1, 3}; 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 A026438 Cf. A026437 and references therein.
%K A026438 nonn
%O A026438 1,2
%A A026438 _Clark Kimberling_
%E A026438 Name clarified by _Robert C. Lyons_, Feb 06 2025