|
|
A363950
|
|
Numbers whose prime indices have rounded-up mean 2.
|
|
12
|
|
|
3, 6, 9, 10, 12, 18, 20, 24, 27, 28, 30, 36, 40, 48, 54, 56, 60, 72, 80, 81, 84, 88, 90, 96, 100, 108, 112, 120, 144, 160, 162, 168, 176, 180, 192, 200, 208, 216, 224, 240, 243, 252, 264, 270, 280, 288, 300, 320, 324, 336, 352, 360, 384, 400, 416, 432, 448
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
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.
|
|
LINKS
|
|
|
EXAMPLE
|
The terms together with their prime indices begin:
3: {2}
6: {1,2}
9: {2,2}
10: {1,3}
12: {1,1,2}
18: {1,2,2}
20: {1,1,3}
24: {1,1,1,2}
27: {2,2,2}
28: {1,1,4}
30: {1,2,3}
36: {1,1,2,2}
40: {1,1,1,3}
48: {1,1,1,1,2}
54: {1,2,2,2}
56: {1,1,1,4}
60: {1,1,2,3}
72: {1,1,1,2,2}
80: {1,1,1,1,3}
81: {2,2,2,2}
|
|
MATHEMATICA
|
prix[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[1000], Ceiling[Mean[prix[#]]]==2&]
|
|
CROSSREFS
|
For mean 1 we have A000079 except 1.
Partitions of this type are counted by A026905 redoubled.
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|