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%I #18 Feb 06 2025 13:51:17
%S 2,4,5,6,8,10,12,13,14,16,17,18,20,21,22,26,28,30,32,34,36,37,38,40,
%T 42,44,45,46,48,50,52,53,54,56,57,58,60,61,62,65,66,68,70,72,74,76,78,
%U 80,81,82,85,86,88,90,92,93,94,96,97,98
%N 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 2,4.
%H Ivan Neretin, <a href="/A026441/b026441.txt">Table of n, a(n) for n = 1..1000</a>
%t a = {2, 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 Cf. A026437 and references therein.
%K nonn
%O 1,1
%A _Clark Kimberling_
%E Name clarified by _Robert C. Lyons_, Feb 06 2025