|
%I #22 Aug 06 2021 02:58:08
%S 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,
%T 45,47,48,50,51,54,55,57,59,60,62,63,65,66,69,71,77,78,81,84,86,87,89,
%U 90,91,93,95,99,101,102,104,105,107,110,111
%N a(n) = least positive integer > a(n-1) and not equal to a(i)*a(j)-2 for 1<=i<j<=n-1.
%H Ivan Neretin, <a href="/A026453/b026453.txt">Table of n, a(n) for n = 1..1000</a>
%e 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
%t 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 *)
%Y Similar sequences with different starting conditions: A026454 (1,3), A026455 (2,3), A026456 (1,4), A026457 (2,4), A026458 (3,4).
%Y 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).
%K nonn
%O 1,2
%A _Clark Kimberling_
%E Typos in definition corrected by _N. J. A. Sloane_, Aug 06 2021 at the suggestion of _Harvey P. Dale_.
|
