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A362639 Number of partitions of [n] whose blocks are ordered with increasing least elements and where block i (except possibly the last) has size i.

%I A362639 #9 May 15 2023 16:38:19
%S A362639 1,1,1,1,2,3,4,15,36,70,120,756,2800,7920,18900,40040,388080,2106000,
%T A362639 8408400,27489000,77837760,197520960,2756754000,20903929200,
%U A362639 113809696000,497097881280,1847907341280,6062876820000,17990209036800,343877493960000,3501594297801600
%N A362639 Number of partitions of [n] whose blocks are ordered with increasing least elements and where block i (except possibly the last) has size i.
%H A362639 Alois P. Heinz, <a href="/A362639/b362639.txt">Table of n, a(n) for n = 0..724</a>
%H A362639 Wikipedia, <a href="https://en.wikipedia.org/wiki/Partition_of_a_set">Partition of a set</a>
%e A362639 a(0) = 1: (), the empty partition.
%e A362639 a(1) = 1: 1.
%e A362639 a(2) = 1: 1|2.
%e A362639 a(3) = 1: 1|23.
%e A362639 a(4) = 2: 1|23|4, 1|24|3.
%e A362639 a(5) = 3: 1|23|45, 1|24|35, 1|25|34.
%e A362639 a(6) = 4: 1|23|456, 1|24|356, 1|25|346, 1|26|345.
%e A362639 a(7) = 15: 1|23|456|7, 1|23|457|6, 1|23|467|5, 1|24|356|7, 1|24|357|6, 1|24|367|5, 1|25|346|7, 1|25|347|6, 1|26|345|7, 1|27|345|6, 1|26|347|5, 1|27|346|5, 1|25|367|4, 1|26|357|4, 1|27|356|4.
%p A362639 b:= proc(n, t) option remember; `if`(n<=t, 1,
%p A362639       b(n-t, t+1)*binomial(n-1, t-1))
%p A362639     end:
%p A362639 a:= n-> b(n, 1):
%p A362639 seq(a(n), n=0..30);
%Y A362639 Cf. A000110, A362637.
%K A362639 nonn
%O A362639 0,5
%A A362639 _Alois P. Heinz_, Apr 28 2023