A304716 - OEIS

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A304716

Number of integer partitions of n whose distinct parts are connected.

1, 2, 2, 3, 2, 5, 2, 6, 4, 9, 3, 15, 4, 18, 12, 25, 11, 41, 17, 54, 36, 72, 44, 113, 69, 145, 113, 204, 153, 302, 220, 394, 343, 541, 475, 771, 662, 1023, 968, 1398, 1314, 1929, 1822, 2566, 2565, 3440, 3446, 4677, 4688, 6187, 6407, 8216, 8544, 10975, 11436

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

OFFSET

1,2

COMMENTS

Given a finite set S of positive integers greater than one, let G(S) be the simple labeled graph with vertex set S and edges between any two vertices with a common divisor. For example, G({6,14,15,35}) is a 4-cycle. A multiset S is said to be connected if G(S) is a connected graph.

LINKS

Table of n, a(n) for n=1..55.

FORMULA

For n > 1, a(n) = A218970(n) + 1. - Gus Wiseman, Dec 04 2018

EXAMPLE

The a(12) = 15 connected integer partitions and their corresponding connected multiset multisystems (see A112798, A302242) are the following.

(12): {{1,1,2}}

(6 6): {{1,2},{1,2}}

(8 4): {{1,1,1},{1,1}}

(9 3): {{2,2},{2}}

(10 2): {{1,3},{1}}

(4 4 4): {{1,1},{1,1},{1,1}}

(6 3 3): {{1,2},{2},{2}}

(6 4 2): {{1,2},{1,1},{1}}

(8 2 2): {{1,1,1},{1},{1}}

(3 3 3 3): {{2},{2},{2},{2}}

(4 4 2 2): {{1,1},{1,1},{1},{1}}

(6 2 2 2): {{1,2},{1},{1},{1}}

(4 2 2 2 2): {{1,1},{1},{1},{1},{1}}

(2 2 2 2 2 2): {{1},{1},{1},{1},{1},{1}}

(1 1 1 1 1 1 1 1 1 1 1 1): {{},{},{},{},{},{},{},{},{},{},{},{}}

MATHEMATICA

zsm[s_]:=With[{c=Select[Tuples[Range[Length[s]], 2], And[Less@@#, GCD@@s[[#]]]>1&]}, If[c==={}, s, zsm[Union[Append[Delete[s, List/@c[[1]]], LCM@@s[[c[[1]]]]]]]]];

Table[Length[Select[IntegerPartitions[n], Length[zsm[Union[#]]]===1&]], {n, 30}]

CROSSREFS

Cf. A000009, A003963, A048143, A054921, A218970, A285572, A286518, A302242, A304714, A305078, A305079, A322306, A322307.

Sequence in context: A066656 A164896 A298422 * A237984 A118136 A356552

Adjacent sequences: A304713 A304714 A304715 * A304717 A304718 A304719

KEYWORD

nonn

AUTHOR

Gus Wiseman, May 17 2018

EXTENSIONS

Name changed to distinguish from A218970 by Gus Wiseman, Dec 04 2018

STATUS

approved