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A274839
Number of set partitions of [n] such that the difference between each element and its block index is a multiple of six.
2
1, 1, 1, 1, 1, 1, 1, 2, 3, 4, 5, 6, 7, 15, 30, 57, 104, 183, 310, 811, 1939, 4377, 9497, 19987, 40883, 121620, 339817, 902822, 2301883, 5665060, 13489425, 44503335, 140080438, 425111779, 1250942834, 3575716011, 9910354002, 36376567529, 127026151621
OFFSET
0,8
LINKS
EXAMPLE
a(7) = 2: 17|2|3|4|5|6, 1|2|3|4|5|6|7.
a(8) = 3: 17|28|3|4|5|6, 1|28|3|4|5|6|7, 1|2|3|4|5|6|7|8.
a(9) = 4: 17|28|39|4|5|6, 1|28|39|4|5|6|7, 1|2|39|4|5|6|7|8, 1|2|3|4|5|6|7|8|9.
MAPLE
b:= proc(n, m, t) option remember; `if`(n=0, 1,
add(`if`(irem(j-t, 6)=0, b(n-1, max(m, j),
irem(t+1, 6)), 0), j=1..m+1))
end:
a:= n-> b(n, 0, 1):
seq(a(n), n=0..40);
MATHEMATICA
b[n_, m_, t_] := b[n, m, t] = If[n == 0, 1, Sum[If[Mod[j - t, 6] == 0, b[n - 1, Max[m, j], Mod[t + 1, 6]], 0], {j, 1, m + 1}]];
a[n_] := b[n, 0, 1];
Table[a[n], {n, 0, 40}] (* Jean-François Alcover, May 15 2018, after Alois P. Heinz *)
CROSSREFS
Column k=6 of A274835.
Sequence in context: A263469 A165804 A055402 * A361809 A367933 A356194
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jul 08 2016
STATUS
approved