A320923 - OEIS

A320923

Heinz numbers of connected graphical partitions.

4, 12, 27, 36, 40, 81, 90, 108, 112, 120, 225, 243, 252, 270, 300, 324, 336, 352, 360, 400, 567, 625, 630, 675, 729, 750, 756, 792, 810, 832, 840, 900, 972, 1000, 1008, 1056, 1080, 1120, 1200, 1323, 1575, 1701, 1750, 1764, 1782, 1872, 1875, 1890, 1980, 2025

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

The Heinz number of an integer partition (y_1, ..., y_k) is prime(y_1) * ... * prime(y_k).

An integer partition is connected and graphical if it comprises the multiset of vertex-degrees of some connected simple graph.

LINKS

Table of n, a(n) for n=1..50.

EXAMPLE

The sequence of all connected-graphical partitions begins: (11), (211), (222), (2211), (3111), (2222), (3221), (22211), (41111), (32111), (3322), (22222), (42211), (32221), (33211), (222211), (421111), (511111), (322111).

MATHEMATICA

prptns[m_]:=Union[Sort/@If[Length[m]==0, {{}}, Join@@Table[Prepend[#, m[[ipr]]]&/@prptns[Delete[m, List/@ipr]], {ipr, Select[Prepend[{#}, 1]&/@Select[Range[2, Length[m]], m[[#]]>m[[#-1]]&], UnsameQ@@m[[#]]&]}]]];

csm[s_]:=With[{c=Select[Tuples[Range[Length[s]], 2], And[OrderedQ[#], UnsameQ@@#, Length[Intersection@@s[[#]]]>0]&]}, If[c=={}, s, csm[Union[Append[Delete[s, List/@c[[1]]], Union@@s[[c[[1]]]]]]]]];

Select[Range[1000], Select[prptns[Flatten[MapIndexed[Table[#2, {#1}]&, If[#==1, {}, Flatten[Cases[FactorInteger[#], {p_, k_}:>Table[PrimePi[p], {k}]]]]]]], And[UnsameQ@@#, Length[csm[#]]==1]&]!={}&]

CROSSREFS

Cf. A000070, A000569, A007717, A025065, A056239, A096373, A112798, A147878, A209816, A300061, A320635, A320911, A320921, A320922, A320925.

Sequence in context: A066185 A330704 A239940 * A008107 A266958 A057306

Adjacent sequences: A320920 A320921 A320922 * A320924 A320925 A320926

KEYWORD

nonn

AUTHOR

Gus Wiseman, Oct 24 2018

STATUS

approved