A026440 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 1,4.

1, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18, 20, 21, 22, 25, 26, 28, 30, 32, 33, 36, 37, 38, 40, 42, 45, 46, 50, 52, 56, 57, 58, 60, 61, 66, 68, 70, 72, 73, 74, 75, 78, 81, 82, 85, 86, 88, 91, 92, 93, 94, 96, 100, 102, 105, 106

Offset

1,2

Links

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

Mathematica

a = {1, 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 *)

Crossrefs

Cf. A026437 and references therein.

Sequence in context: A181708 A026456 A026425 * A299487 A063713 A026462

Adjacent sequences: A026437 A026438 A026439 * A026441 A026442 A026443

Keyword

nonn,changed

Author

Clark Kimberling

Extensions

Name clarified by Robert C. Lyons, Feb 06 2025

Status

approved