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a(n) is the difference between the two smallest positive integers that you cannot obtain using the integers {1,2,...,n} at most once and the four operators +, -, *, /.
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%I #9 Dec 29 2022 06:46:25

%S 1,1,1,2,3,23,5,144,98,658

%N a(n) is the difference between the two smallest positive integers that you cannot obtain using the integers {1,2,...,n} at most once and the four operators +, -, *, /.

%H Gilles Bannay, <a href="https://web.archive.org/web/20061201125224/http://gilles.bannay.free.fr/jeux_us.html">Countdown Problem</a>

%H <a href="/index/Fo#4x4">Index entries for similar sequences</a>

%e a(4)=2 because 29 and 31 are the smallest numbers that you cannot obtain using {1,2,3,4} and the four operations and 31-29 = 2.

%Y Cf. A060315.

%K hard,more,nonn

%O 1,4

%A Koksal Karakus (karakusk(AT)hotmail.com), Jun 07 2002