A071110 a(n) is the smallest integer >=0 we cannot obtain from n, n+1, n+2, n+3, n+4 and the operators +, -, *, /, using each number only once.

29, 76, 141, 172, 193, 197, 205, 211, 245, 181, 162, 85, 86, 69, 71, 61, 62, 67, 52, 53, 58, 58, 58, 59, 62, 45, 46, 49, 20, 51, 7, 22, 10, 7, 10, 7, 7, 7, 7, 15, 12, 13, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 10, 7, 7, 7, 7, 7, 7, 10, 7, 7, 7, 7, 7, 7, 7, 7, 7

Offset

0,1

Comments

It seems that a(n)=7 for all n>=62, but this needs to be proved.

Links

Table of n, a(n) for n=0..70.

Gilles Bannay, Countdown Problem

Example

a(61)=10 because by using 61, 62, 63, 64, 65 we can get 62-61=1, 63-61=2, ..., 63/((64-61)*(65-62))=7, (65-61)*(64+62)/63=8, (65-62)*(64-61)=9 but we cannot obtain 10 in the same way.
a(32) != 7 because 7 = 35 / (34 - (32 - (36 - 33))). - Sean A. Irvine, Jun 30 2024

Crossrefs

Cf. A060316.

Sequence in context: A161617 A142305 A184072 * A263534 A273360 A176185

Adjacent sequences: A071107 A071108 A071109 * A071111 A071112 A071113

Keyword

nonn

Author

Koksal Karakus (karakusk(AT)hotmail.com), May 27 2002

Extensions

a(32) and a(40) corrected by Sean A. Irvine, Jun 30 2024

Status

approved