A026437 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 1,2.

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, 42, 44, 45, 46, 48, 50, 52, 53, 54, 56, 57, 58, 60, 61, 62, 65, 66, 68, 70, 72, 74, 76, 78, 80, 81, 82, 85, 86, 88, 90, 92, 93, 94, 96, 97

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Links

• Ivan Neretin, Table of n, a(n) for n = 1..1000

Crossrefs

Similar sequences with different starting conditions: A026438 (1,3), A026439 (2,3), A026440 (1,4), A026441 (2,4), A026442 (3,4).

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

Programs

Mathematica

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 *)

Extensions

Terms corrected by Ivan Neretin, Feb 15 2018

Name clarified by Robert C. Lyons, Feb 06 2025