A272517 - OEIS

%I #7 Dec 11 2020 08:18:19

%S 37837800,100900800,588107520,2977294320,20020160160,164118754800,

%T 635661248040,3295178686800,17741374681800,95826446465904,

%U 623399389674600,2664090278249400,13876038856379700,71797074694745400,375274098870636420,2199911433079733100

%N Number of set partitions of [n] into five blocks with distinct sizes.

%H Alois P. Heinz, <a href="/A272517/b272517.txt">Table of n, a(n) for n = 15..1000</a>

%F a(n) = n! * [x^n*y^5] Product_{n>=1} (1+y*x^n/n!).

%p b:= proc(n, i, t) option remember; `if`(t>i or t*(t+1)/2>n

%p       or t*(2*i+1-t)/2<n, 0, `if`(n=0, 1, b(n,i-1,t)+

%p       `if`(i>n, 0, b(n-i, i-1, t-1)*binomial(n,i))))

%p     end:

%p a:= n-> b(n$2, 5):

%p seq(a(n), n=15..40);

%t b[n_, i_, t_] := b[n, i, t] = If[t > i || t(t+1)/2 > n || t(2i+1-t)/2 < n, 0, If[n == 0, 1, b[n, i - 1, t] + If[i > n, 0, b[n - i, i - 1, t - 1]* Binomial[n, i]]]];

%t a[n_] := b[n, n, 5];

%t a /@ Range[15, 40] (* _Jean-François Alcover_, Dec 11 2020, after _Alois P. Heinz_ *)

%Y Column k=5 of A131632.

%K nonn

%O 15,1

%A _Alois P. Heinz_, May 01 2016