cp's OEIS Frontend

A301480 Number of rooted twice-partitions of n.

%I A301480 #11 Aug 29 2018 02:52:26
%S A301480 1,1,2,4,8,15,30,54,103,186,345,606,1115,1936,3466,6046,10630,18257,
%T A301480 31927,54393,93894,159631,272155,458891,779375,1305801,2196009,
%U A301480 3667242,6130066,10170745,16923127,27942148,46211977,76039205,125094369,204952168,335924597
%N A301480 Number of rooted twice-partitions of n.
%C A301480 A rooted partition of n is an integer partition of n - 1. A rooted twice-partition of n is a choice of a rooted partition of each part in a rooted partition of n.
%H A301480 Andrew Howroyd, <a href="/A301480/b301480.txt">Table of n, a(n) for n = 1..500</a>
%F A301480 O.g.f.: x * Product_{n > 0} 1/(1 - P(n-1) x^n) where P = A000041.
%e A301480 The a(5) = 8 rooted twice-partitions: ((3)), ((21)), ((111)), ((2)()), ((11)()), ((1)(1)), ((1)()()), (()()()()).
%e A301480 The a(6) = 15 rooted twice-partitions:
%e A301480 (4), (31), (22), (211), (1111),
%e A301480 (3)(), (21)(), (111)(), (2)(1), (11)(1),
%e A301480 (2)()(), (11)()(), (1)(1)(),
%e A301480 (1)()()(),
%e A301480 ()()()()().
%t A301480 nn=30;
%t A301480 ser=x*Product[1/(1-PartitionsP[n-1]x^n),{n,nn}];
%t A301480 Table[SeriesCoefficient[ser,{x,0,n}],{n,nn}]
%o A301480 (PARI) seq(n)={Vec(1/prod(k=1, n-1, 1 - numbpart(k-1)*x^k + O(x^n)))} \\ _Andrew Howroyd_, Aug 29 2018
%Y A301480 Cf. A001383, A002865, A032305, A063834, A093637, A127524, A196545, A220418, A281113, A289501, A301422, A301462, A301467.
%K A301480 nonn
%O A301480 1,3
%A A301480 _Gus Wiseman_, Mar 22 2018