A379843 Least number x such that there are exactly n sets of positive integers > 1 with sum + product = x. Position of first appearance of n in A379679.

2, 1, 14, 44, 47, 89, 119, 179, 159, 239, 335, 539, 599, 744, 359, 719, 839

Offset

0,1

Comments

Warning: Do not confuse with the multiset version A379543.

Links

Table of n, a(n) for n=0..16.

Example

We have a(4) = 47 due to the following four sets: {5,7}, {2,15}, {3,11}, {2,3,6}.

Mathematica

nn=100;
strfacs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[strfacs[n/d], Min@@#>d&]], {d, Rest[Divisors[n]]}]];
mnrm[s_]:=If[Min@@s==1, mnrm[DeleteCases[s-1, 0]]+1, 0];
s=Table[Length[Select[Join@@Array[strfacs, n], Total[#]+Times@@#==n&]], {n, nn}];
Table[Position[s, k-1][[1, 1]], {k, mnrm[s+1]}]

Crossrefs

For multisets instead of sets we have A379543, firsts of A379669.

Positions of first appearances in A379679, see A379842.

Arrays counting multisets by sum and product:

- partitions: A379666, antidiagonal sums A379667

- partitions without ones: A379668, antidiagonal sums A379669

- strict partitions: A379671, antidiagonal sums A379672

- strict partitions without ones: A379678, antidiagonal sums A379679.

A000041 counts integer partitions, strict A000009.

A001055 counts integer factorizations, strict A045778.

A002865 counts partitions into parts > 1, strict A025147.

A318950 counts factorizations by sum.

Cf. A069016, A111133, A319000, A319057, A379670, A379680, A379720, A379839, A379840, A379841.

Sequence in context: A106204 A290603 A083074 * A346378 A181869 A141510

Adjacent sequences: A379840 A379841 A379842 * A379844 A379845 A379846

Keyword

nonn,more

Author

Gus Wiseman, Jan 15 2025

Status

approved