A026437 - OEIS

%I #12 Feb 23 2018 09:12:16

%S 1,2,4,5,6,8,10,12,13,14,16,17,18,20,21,22,26,28,30,32,34,36,37,38,40,

%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

%N a(n) = least positive integer > a(n-1) and not a(i)*a(j)-1 for 1 <= i <= j < n, n >= 2.

%H Ivan Neretin, <a href="/A026437/b026437.txt">Table of n, a(n) for n = 1..1000</a>

%t a = {1, 2}; 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 Similar sequences with different starting conditions: A026438 (1,3), A026439 (2,3), A026440 (1,4), A026441 (2,4), A026442 (3,4).

%Y Related sequences with definition using distinct i,j: A026431 and references therein.

%K nonn

%O 1,2

%A _Clark Kimberling_

%E Terms corrected by _Ivan Neretin_, Feb 15 2018