A026453 - OEIS

A026453

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

1, 2, 3, 5, 6, 7, 9, 11, 14, 15, 17, 18, 21, 22, 23, 24, 27, 29, 30, 35, 36, 37, 38, 39, 41, 45, 47, 48, 50, 51, 54, 55, 57, 59, 60, 62, 63, 65, 66, 69, 71, 77, 78, 81, 84, 86, 87, 89, 90, 91, 93, 95, 99, 101, 102, 104, 105, 107, 110, 111

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

OFFSET

1,2

LINKS

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

EXAMPLE

After the terms 1, 2, 3, 5, 6, 7, we can get 8 from 2*5 - 2, but not 9 (11 is not a product of two distinct terms from {1, 2, 3, 5, 6, 7}), so a(7) = 9. - N. J. A. Sloane, Aug 06 2021

MATHEMATICA

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

CROSSREFS

Similar sequences with different starting conditions: A026454 (1,3), A026455 (2,3), A026456 (1,4), A026457 (2,4), A026458 (3,4).

Related sequences with definition using any products (not necessarily distinct) and with various starting conditions: A026459 (1,2), A026460 (1,3), A026461 (2,3), A026462 (1,4), A026463 (2,4), A026464 (3,4).

Sequence in context: A392070 A376471 A358221 * A026455 A082984 A085717

Adjacent sequences: A026450 A026451 A026452 * A026454 A026455 A026456

KEYWORD

nonn

AUTHOR

Clark Kimberling

EXTENSIONS

Typos in definition corrected by N. J. A. Sloane, Aug 06 2021 at the suggestion of Harvey P. Dale.

STATUS

approved