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%I #18 Feb 08 2023 10:59:17
%S 284,307,309,314,317,379,394,398,403,411,417,423,429,431,433,435,436,
%T 437,439,441,442,443,445,446,447,449,451,453,454,457,458,459,461,463,
%U 464,466,467,469,471,473,474,487,489,491,493,494,496,499,502,506,509
%N Numbers which cannot be reached in the Countdown Numbers Game starting from (1,2,3,4,5,6): the game allows brackets and the operations + - x and / and not all numbers need be used, while the result of each partial calculation must be an integer.
%C Starting with (1,1,1,1,1,1) no number greater than 9 can be reached.
%C Every number greater than 1080 = 6*5*4*3*(2+1) is in the sequence. - _Sean A. Irvine_, Feb 07 2023
%H Michael S. Branicky, <a href="/A061310/b061310.txt">Table of n, a(n) for n = 1..538</a> (all terms < 1081)
%H Henry Bottomley, <a href="http://www.se16.info/js/cdown.htm">Countdown Numbers Game applet</a>
%H Michael S. Branicky, <a href="/A061310/a061310.py.txt">Python program</a>
%H <a href="/index/Fo#4x4">Index entries for similar sequences</a>
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%e 283 is not in the sequence since 283=((6+1)*5*4*2)+3; 285 is not in the sequence since 285=((6*5*2)-3)*(4+1). However there is no similar calculation for 284 so 284 is in the sequence.
%K nonn,easy
%O 1,1
%A _Henry Bottomley_, Jun 05 2001
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