OFFSET
1,1
COMMENTS
Omega(a(n)) = Omega(a(n) - Omega(a(n))) because Omega(a(n)) = 2, and a(n) - 2 is semiprime => this sequence is a subsequence of A200925.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Semiprime
FORMULA
a(n) = A092207(n) + 2.
MATHEMATICA
PrimeFactorExponentsAdded[n_] := Plus @@ Flatten[Table[ #[[2]], {1}] & /@ FactorInteger[n]]; Select[ Range[ 671], PrimeFactorExponentsAdded[ # ] == PrimeFactorExponentsAdded[ # - 2] == 2 &]
SemiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; Select[Range[1000], SemiPrimeQ[#] && SemiPrimeQ[# - 2] &] (* T. D. Noe, Nov 27 2011 *)
#[[3, 1]]&/@Select[Partition[Table[{n, PrimeOmega[n]}, {n, 700}], 3, 1], #[[1, 2]]==#[[3, 2]]==2&] (* Harvey P. Dale, Dec 10 2011 *)
CROSSREFS
KEYWORD
nonn,changed
AUTHOR
Michel Lagneau, Nov 25 2011
STATUS
approved