A026442 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.

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, 46, 50, 52, 54, 55, 56, 57, 58, 60, 61, 66, 67, 68, 70, 72, 73, 75, 76, 78, 81, 82, 84, 85, 86, 88, 91, 93, 94, 96, 97, 100, 101, 102, 103, 105

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Comments

a(n) = A026438(n+1) for n > 1. - Georg Fischer, Oct 22 2018

Links

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

Crossrefs

Cf. A026437 and references therein.

Cf. A026438.

Programs

Mathematica

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 *)

Extensions

Name clarified by Robert C. Lyons, Feb 06 2025