A026440 - OEIS

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A026440

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

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

(list; graph; refs; listen; history; text; internal format)

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

AUTHOR

Clark Kimberling

STATUS

approved