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A295390
Number T(n,k) of permutations of [n] having exactly k consecutive 3-term arithmetic progressions; triangle T(n,k), n>=0, 0<=k<=max(n-2,0), read by rows.
3
1, 1, 2, 4, 2, 18, 4, 2, 80, 34, 4, 2, 482, 196, 36, 4, 2, 3280, 1418, 292, 44, 4, 2, 26244, 11292, 2426, 304, 48, 4, 2, 231148, 106132, 22156, 3010, 372, 56, 4, 2, 2320130, 1046176, 225804, 32308, 3892, 424, 60, 4, 2, 25238348, 11679626, 2585080, 366484, 42176, 4540, 472, 68, 4, 2
OFFSET
0,3
EXAMPLE
Triangle T(n,k) begins:
1;
1;
2;
4, 2;
18, 4, 2;
80, 34, 4, 2;
482, 196, 36, 4, 2;
3280, 1418, 292, 44, 4, 2;
26244, 11292, 2426, 304, 48, 4, 2;
231148, 106132, 22156, 3010, 372, 56, 4, 2;
2320130, 1046176, 225804, 32308, 3892, 424, 60, 4, 2;
...
CROSSREFS
Column k=0 gives A295370.
Row sums give A000142.
Sequence in context: A326723 A227924 A100944 * A059890 A295640 A210457
KEYWORD
nonn,tabf
AUTHOR
Alois P. Heinz, Nov 21 2017
STATUS
approved