A322337 - OEIS

A322337

Number of strict 2-edge-connected integer partitions of n.

0, 0, 0, 0, 0, 1, 0, 1, 1, 2, 0, 4, 0, 4, 3, 5, 0, 9, 0, 10, 5, 11, 1, 18, 3, 17, 8, 22, 3, 35, 5, 32, 17, 39, 16, 59, 14, 58, 33, 75, 28, 103, 35, 106, 71, 125, 63, 174, 81, 192, 127, 220, 130, 294, 170, 325, 237, 378, 257, 504

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OFFSET

1,10

COMMENTS

An integer partition is 2-edge-connected if the hypergraph of prime factorizations of its parts is connected and cannot be disconnected by removing any single part.

LINKS

Table of n, a(n) for n=1..60.

Wikipedia, k-edge-connected graph

EXAMPLE

The a(24) = 18 strict 2-edge-connected integer partitions of 24:

(15,9) (10,8,6) (10,8,4,2)

(16,8) (12,8,4) (12,6,4,2)

(18,6) (12,9,3)

(20,4) (14,6,4)

(21,3) (14,8,2)

(22,2) (15,6,3)

(14,10) (16,6,2)

(18,4,2)

(12,10,2)

MATHEMATICA

primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];

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

twoedQ[sys_]:=And[Length[csm[sys]]==1, And@@Table[Length[csm[Delete[sys, i]]]==1, {i, Length[sys]}]];

Table[Length[Select[IntegerPartitions[n], And[UnsameQ@@#, twoedQ[primeMS/@#]]&]], {n, 30}]

CROSSREFS

Cf. A007718, A013922, A054921, A095983, A218970, A275307, A286518, A304714, A304716, A305078, A305079, A322335, A322336.

Sequence in context: A337605 A082024 A337599 * A211008 A365344 A366543

Adjacent sequences: A322334 A322335 A322336 * A322338 A322339 A322340

KEYWORD

nonn

AUTHOR

Gus Wiseman, Dec 04 2018

STATUS

approved