A367397 Numbers m such that bigomega(m) is the sum of prime indices of some semiprime divisor of m.

4, 12, 18, 30, 36, 40, 42, 54, 60, 66, 78, 81, 90, 100, 102, 112, 114, 120, 126, 135, 138, 140, 150, 168, 174, 180, 186, 189, 198, 210, 220, 222, 225, 234, 246, 250, 252, 258, 260, 270, 280, 282, 297, 300, 306, 315, 318, 330, 336, 340, 342, 350, 351, 352, 354

Offset

1,1

Comments

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

These are the Heinz numbers of the partitions counted by A367394.

Links

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

Mathematica

prix[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[100], MemberQ[Total/@Subsets[prix[#], {2}], PrimeOmega[#]]&]

Crossrefs

The following sequences count and rank integer partitions and finite sets according to whether their length is a subset-sum, linear combination, or semi-sum of the parts. The current sequence is starred.

sum-full sum-free comb-full comb-free semi-full semi-free

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partitions: A367212 A367213 A367218 A367219 A367394 A367398

strict: A367214 A367215 A367220 A367221 A367395 A367399

subsets: A367216 A367217 A367222 A367223 A367396 A367400

ranks: A367224 A367225 A367226 A367227 A367397* A367401

A325761 ranks partitions whose length is a part, counted by A002865.

A088809 and A093971 count subsets containing semi-sums.

A236912 counts partitions with no semi-sum of the parts, ranks A364461.

A237113 counts partitions with a semi-sum of the parts, ranks A364462.

A304792 counts subset-sums of partitions, strict A365925.

A366738 counts semi-sums of partitions, strict A366741.

Triangles:

A365381 counts subsets with a subset summing to k, complement A366320.

A365541 counts subsets with a semi-sum k.

A367404 counts partitions with a semi-sum k, strict A367405.

Cf. A000700, A229816, A237667, A237668, A238628, A363225, A364272, A365543, A365658, A365918, A366740.

Sequence in context: A071929 A008037 A301251 * A062859 A300745 A305240

Adjacent sequences: A367394 A367395 A367396 * A367398 A367399 A367400

Keyword

nonn

Author

Gus Wiseman, Nov 21 2023

Status

approved