A026442 - OEIS

%I #22 Feb 06 2025 13:51:13

%S 3,4,5,6,7,9,10,12,13,16,18,21,22,25,28,30,31,32,33,36,37,40,42,43,45,

%T 46,50,52,54,55,56,57,58,60,61,66,67,68,70,72,73,75,76,78,81,82,84,85,

%U 86,88,91,93,94,96,97,100,101,102,103,105

%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 3,4.

%C a(n) = A026438(n+1) for n > 1. - _Georg Fischer_, Oct 22 2018

%H Ivan Neretin, <a href="/A026442/b026442.txt">Table of n, a(n) for n = 1..1000</a>

%t a = {3, 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.

%Y Cf. A026438.

%K nonn

%O 1,1

%A _Clark Kimberling_

%E Name clarified by _Robert C. Lyons_, Feb 06 2025