Strict Arrangements
How many ways are there to arrange the digits 1 to 7 in a line such that no three consecutive digits are ascending?
For example:
-
7132564 contains three consecutive ascending digits since 2<5<6.
-
3215476 does not contain three consecutive ascending digits.
The answer is 2017.
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1 solution
Mathematica
Length@Select[Permutations[Range@7],!Or@@OrderedQ/@Partition[#,3,1]&]2017