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 A240085 Number of compositions of n in which no part is unique (every part appears at least twice). 7

%I

%S 1,0,1,1,2,1,9,11,34,53,108,169,400,680,1530,2984,6362,12498,25766,

%T 50093,102126,199309,400288,788227,1581584,3135117,6286310,12532861,

%U 25121292,50184582,100627207,201208477,403170900,806534560,1615151111,3231224804,6467909442

%N Number of compositions of n in which no part is unique (every part appears at least twice).

%D S. Heubach and T. Mansour, Combinatorics of Compositions and Words, Chapman and Hall, 2009.

%H Alois P. Heinz and Vaclav Kotesovec, <a href="/A240085/b240085.txt">Table of n, a(n) for n = 0..2100</a> (first 500 terms from Alois P. Heinz)

%H Vaclav Kotesovec, <a href="/A240085/a240085.jpg">Graph a(n)/2^n</a>

%e a(6) = 9 because we have: 3+3, 2+2+2, 2+2+1+1, 2+1+2+1, 2+1+1+2, 1+2+2+1, 1+2+1+2, 1+1+2+2, 1+1+1+1+1+1.

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

%p b(n, i-1, t) +add(b(n-i*j, i-1, t+j)/j!, j=2..n/i)))

%p end:

%p a:= n-> b(n\$2, 0):

%p seq(a(n), n=0..40); # _Alois P. Heinz_, Mar 31 2014

%t Table[Length[Level[Map[Permutations,Select[IntegerPartitions[n], Apply[And,Table[Count[#,#[[i]]]>1,{i,1,Length[#]}]]&]],{2}]],{n,0,20}]

%t (* Second program: *)

%t b[n_, i_, t_] := b[n, i, t] = If[n == 0, t!, If[i < 1, 0, b[n, i - 1, t] + Sum[b[n - i*j, i - 1, t + j]/j!, {j, 2, n/i}]]]; a[n_] := b[n, n, 0]; Table[a[n], {n, 0, 40}] (* _Jean-François Alcover_, Aug 29 2016, after _Alois P. Heinz_ *)

%Y Cf. A007690.

%K nonn

%O 0,5

%A _Geoffrey Critzer_, Mar 31 2014

%E More terms from _Alois P. Heinz_, Mar 31 2014

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Last modified June 1 04:57 EDT 2020. Contains 334758 sequences. (Running on oeis4.)