+0  
 
+1
379
2
avatar+637 

A number is formed using the digits 1, 2, ..., 9. Any digit can be used more than once, but adjacent digits cannot be the same. Once a pair of adjacent digits has occurred, that pair, in that order, cannot be used again. How many digits are in the largest such number. 

 Nov 2, 2017
 #1
avatar+17747 
+2

I think that the answer is 73: 

 

98 97 96 95 94 93 92 91 87 86 85 84 83 82 81 76 75 74 73 72 71 65 64 63 62 61 54 53 52 51 43 42 41 32 31 21 9

 Nov 2, 2017
 #2
avatar+637 
+1

Thanks!

 Nov 3, 2017

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