OFFSET
1,1
EXAMPLE
The sequence of terms together with their prime indices begins:
9: {2,2} 169: {6,6} 319: {5,10}
21: {2,4} 183: {2,18} 321: {2,28}
25: {3,3} 185: {3,12} 339: {2,30}
39: {2,6} 203: {4,10} 361: {8,8}
49: {4,4} 213: {2,20} 365: {3,21}
57: {2,8} 235: {3,15} 371: {4,16}
65: {3,6} 237: {2,22} 377: {6,10}
87: {2,10} 247: {6,8} 393: {2,32}
91: {4,6} 259: {4,12} 417: {2,34}
111: {2,12} 267: {2,24} 427: {4,18}
115: {3,9} 289: {7,7} 445: {3,24}
121: {5,5} 299: {6,9} 453: {2,36}
129: {2,14} 301: {4,14} 481: {6,12}
133: {4,8} 303: {2,26} 489: {2,38}
159: {2,16} 305: {3,18} 497: {4,20}
MATHEMATICA
Select[Range[100], PrimeOmega[#]==2&&GCD@@PrimePi/@First/@FactorInteger[#]>1&]
CROSSREFS
A339002 is the squarefree case.
A001221 counts distinct prime indices.
A001222 counts prime indices.
A318990 lists semiprimes with divisible indices.
A320655 counts factorizations into semiprimes.
A338910 lists semiprimes with odd indices.
A338911 lists semiprimes with even indices.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Nov 20 2020
STATUS
approved