This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A142153 #23 May 30 2018 05:06:10
%S A142153 1,2,5,18,87,451
%N A142153 a(n) is the "highest smallest" positive integer that cannot be obtained from the (n-1) optimized integers (to be defined for each n) using each number at most once and the operators +, -, *, /.
%C A142153 This sequence is a kind of optimized version of the sequence A060315 for which the inputs are the integers {0,1,...,n-1}. Here the inputs are optimized so that the smallest positive integer, that cannot be obtained, is maximized.
%C A142153 Further terms may be hard to find. Some additional terms (still to be proved) could be a(7)=3495, a(8)=32355, a(9)=384289. If anyone has found higher numbers please contact me. - updated by _Gilles A.Fleury_, Jul 10 2017 and May 22 2018
%e A142153 a(4) = 18 because every integer can be calculated up to 17, using one of the four (!) optimal sequences {2,3,10} or {2,3,14} or {2,6,11} or {2,6,13}.
%e A142153 a(5) = 87 because every integer can be calculated up to 86, using the optimal numbers {2,3,14,60}.
%e A142153 a(6) = 451 because every integer can be calculated up to 450, using the optimal numbers {2,3,4,63,152}. - _Gilles A.Fleury_, Mar 06 2009
%Y A142153 Cf. A141494, A060315.
%K A142153 hard,nonn
%O A142153 1,2
%A A142153 _Gilles A.Fleury_, Oct 05 2008
%E A142153 a(6) from _Gilles A.Fleury_, Mar 06 2009