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.
EXAMPLE
The terms together with their prime indices begin:
4: {1,1} 94: {1,15} 214: {1,28}
6: {1,2} 106: {1,16} 218: {1,29}
10: {1,3} 118: {1,17} 225: {2,2,3,3}
14: {1,4} 122: {1,18} 226: {1,30}
22: {1,5} 134: {1,19} 254: {1,31}
26: {1,6} 135: {2,2,2,3} 262: {1,32}
34: {1,7} 142: {1,20} 274: {1,33}
38: {1,8} 146: {1,21} 278: {1,34}
46: {1,9} 158: {1,22} 297: {2,2,2,5}
58: {1,10} 166: {1,23} 298: {1,35}
62: {1,11} 178: {1,24} 302: {1,36}
74: {1,12} 189: {2,2,2,4} 314: {1,37}
81: {2,2,2,2} 194: {1,25} 315: {2,2,3,4}
82: {1,13} 202: {1,26} 326: {1,38}
86: {1,14} 206: {1,27} 334: {1,39}
MATHEMATICA
prix[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[100], Length[prix[#]]==2*Min[prix[#]]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jun 05 2023
STATUS
approved