A063834 Twice partitioned numbers: the number of ways a number can be partitioned into not necessarily different parts and each part is again so partitioned.

1, 1, 3, 6, 15, 28, 66, 122, 266, 503, 1027, 1913, 3874, 7099, 13799, 25501, 48508, 88295, 165942, 299649, 554545, 997281, 1817984, 3245430, 5875438, 10410768, 18635587, 32885735, 58399350, 102381103, 180634057, 314957425, 551857780, 958031826, 1667918758

Offset

0,3

Comments

These are different from plane partitions.

For ordered partitions of partitions see A055887 which may be computed from A036036 and A048996. - Alford Arnold, May 19 2006

Twice partitioned numbers correspond to triangles (or compositions) in the multiorder of integer partitions. - Gus Wiseman, Oct 28 2015

Links

Alois P. Heinz, Table of n, a(n) for n = 0..5000 (terms n=1..500 from T. D. Noe)

Vaclav Kotesovec, Screenshot - A closed form formula for the constant c

Gus Wiseman, Comcategories and Multiorders (pdf version)

Gus Wiseman, On the Categorical Structure of Weakly Ordered Sequences of Integer Partitions

Gus Wiseman, Sequences enumerating triangles of integer partitions

Formula

G.f.: 1/Product_{k>0} (1-A000041(k)*x^k). n*a(n) = Sum_{k=1..n} b(k)*a(n-k), a(0) = 1, where b(k) = Sum_{d|k} d*A000041(d)^(k/d) = 1, 5, 10, 29, 36, 110, 106, ... . - Vladeta Jovovic, Jun 19 2003

From Vaclav Kotesovec, Mar 27 2016: (Start)

a(n) ~ c * 5^(n/4), where

c = 96146522937.7161898848278970039269600938032826... if n mod 4 = 0

c = 96146521894.9433858914667933636782092683849082... if n mod 4 = 1

c = 96146522937.2138934755566928890704687838407524... if n mod 4 = 2

c = 96146521894.8218716328341714149619262713426755... if n mod 4 = 3

(End)

Example

G.f. = 1 + x + 3*x^2 + 6*x^3 + 15*x^4 + 28*x^5 + 66*x^6 + 122*x^7 + 266*x^8 + ...
If n=6, a possible first partitioning is (3+3), resulting in the following second partitionings: ((3),(3)), ((3),(2+1)), ((3),(1+1+1)), ((2+1),(3)), ((2+1),(2+1)), ((2+1),(1+1+1)), ((1+1+1),(3)), ((1+1+1),(2+1)), ((1+1+1),(1+1+1)).

Maple

with(combinat):
b:= proc(n, i) option remember; `if`(n=0 or i=1, 1,
      b(n, i-1)+`if`(i>n, 0, numbpart(i)*b(n-i, i)))
    end:
a:= n-> b(n$2):
seq(a(n), n=0..50);  # Alois P. Heinz, Nov 26 2015

Mathematica

Table[Plus @@ Apply[Times, IntegerPartitions[i] /. i_Integer :> PartitionsP[i], 2], {i, 36}]
(* second program: *)
b[n_, i_] := b[n, i] = If[n==0 || i==1, 1, b[n, i-1] + If[i > n, 0, PartitionsP[i]*b[n-i, i]]]; a[n_] := b[n, n]; Table[a[n], {n, 0, 50}] (* Jean-François Alcover, Jan 20 2016, after Alois P. Heinz *)

Prog

(PARI) {a(n) = if( n<0, 0, polcoeff( 1 / prod(k=1, n, 1 - numbpart(k) * x^k, 1 + x * O(x^n)), n))}; /* Michael Somos, Dec 19 2016 */

Crossrefs

Cf. A063835, A196545.

Cf. A036036, A048996, A055887.

Cf. A006906, A270995.

Cf. A007425, A047966, A047968, A271619, A279375, A279784-A279791.

Row sums of A321449.

Column k=2 of A323718.

Cf. A327769.

Sequence in context: A318396 A034953 A086737 * A139117 A226736 A066708

Adjacent sequences: A063831 A063832 A063833 * A063835 A063836 A063837

Keyword

nonn,nice

Author

Wouter Meeussen, Aug 21 2001

Extensions

a(0)=1 prepended by Alois P. Heinz, Nov 26 2015

Status

approved