A026431 a(n) = least positive integer > a(n-1) and not a(i)*a(j)-1 for 1<=i<j<=n, with initial terms 1,2.

1, 2, 3, 4, 6, 8, 9, 10, 12, 13, 14, 16, 18, 20, 21, 22, 24, 28, 30, 32, 33, 34, 36, 37, 40, 42, 44, 45, 46, 48, 49, 50, 52, 54, 56, 57, 58, 60, 61, 64, 66, 68, 69, 70, 72, 74, 75, 76, 78, 80, 81, 82, 84, 85, 86, 88, 90, 92, 93, 94

Offset

1,2

Links

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

Mathematica

a = {1, 2}; used = {a[[1]]*a[[2]] - 1}; Do[k = a[[-1]] + 1; While[MemberQ[used, k], k++]; used = Union[used, k*a - 1]; AppendTo[a, k], {n, 3, 60}]; a (* Ivan Neretin, Mar 06 2016 *)

Crossrefs

Similar sequences with different starting conditions: A026432 (1,3), A026433 (2,3), A026434 (1,4), A026435 (2,4), A026436 (3,4).

Sequence in context: A377078 A352968 A156657 * A026433 A354148 A015858

Adjacent sequences: A026428 A026429 A026430 * A026432 A026433 A026434

Keyword

nonn

Author

Clark Kimberling

Extensions

Name clarified by Robert C. Lyons, Feb 06 2025

Status

approved