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 A274838 Number of set partitions of [n] such that the difference between each element and its block index is a multiple of five. 2

%I

%S 1,1,1,1,1,1,2,3,4,5,6,13,26,49,88,151,397,951,2145,4633,9643,28898,

%T 80843,214126,542081,1317924,4392295,13871122,41984457,122463762,

%U 344409561,1273659431,4463980333,14994032599,48610148069,152506484015,614168698264

%N Number of set partitions of [n] such that the difference between each element and its block index is a multiple of five.

%H Alois P. Heinz, <a href="/A274838/b274838.txt">Table of n, a(n) for n = 0..808</a>

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Partition_of_a_set">Partition of a set</a>

%e a(7) = 3: 16|27|3|4|5, 1|27|3|4|5|6, 1|2|3|4|5|6|7.

%e a(8) = 4: 16|27|38|4|5, 1|27|38|4|5|6, 1|2|38|4|5|6|7, 1|2|3|4|5|6|7|8.

%e a(9) = 5: 16|27|38|49|5, 1|27|38|49|5|6, 1|2|38|49|5|6|7, 1|2|3|49|5|6|7|8, 1|2|3|4|5|6|7|8|9.

%p b:= proc(n, m, t) option remember; `if`(n=0, 1,

%p add(`if`(irem(j-t, 5)=0, b(n-1, max(m, j),

%p irem(t+1, 5)), 0), j=1..m+1))

%p end:

%p a:= n-> b(n, 0, 1):

%p seq(a(n), n=0..40);

%t b[n_, m_, t_] := b[n, m, t] = If[n == 0, 1, Sum[If[Mod[j - t, 5] == 0, b[n - 1, Max[m, j], Mod[t + 1, 5]], 0], {j, 1, m + 1}]];

%t a[n_] := b[n, 0, 1];

%t Table[a[n], {n, 0, 40}] (* _Jean-François Alcover_, May 15 2018, after _Alois P. Heinz_ *)

%Y Column k=5 of A274835.

%K nonn

%O 0,7

%A _Alois P. Heinz_, Jul 08 2016

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Last modified May 21 19:42 EDT 2022. Contains 353929 sequences. (Running on oeis4.)