OFFSET
1,1
COMMENTS
These appear to be all positive integers with prime signature (2,2), (2,1,1), (1,2,1), or (1,1,2).
EXAMPLE
The sequence of terms together with their prime indices begins:
36: {1,1,2,2}
60: {1,1,2,3}
84: {1,1,2,4}
90: {1,2,2,3}
100: {1,1,3,3}
126: {1,2,2,4}
132: {1,1,2,5}
140: {1,1,3,4}
150: {1,2,3,3}
156: {1,1,2,6}
196: {1,1,4,4}
198: {1,2,2,5}
204: {1,1,2,7}
220: {1,1,3,5}
225: {2,2,3,3}
228: {1,1,2,8}
234: {1,2,2,6}
260: {1,1,3,6}
276: {1,1,2,9}
MATHEMATICA
Select[Range[100], DivisorSigma[0, #]-3==(PrimeOmega[#]-1)*PrimeNu[#]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Nov 02 2019
STATUS
approved