OFFSET
1,3
LINKS
Robert G. Wilson v, Table of n, a(n) for n=1..1000
MATHEMATICA
semiPrimeQ[n_] := Plus @@ Last /@ FactorInteger[n] == 2; lst1 = Select[ Range@ 325, semiPrimeQ@# &]; lst = Select[ Range@ 500, semiPrimeQ@# &]; lst - (NextPrime[ #, -1] & /@ lst) (* Robert G. Wilson v, Mar 16 2009 *)
#-NextPrime[#, -1]&/@Select[Range[400], PrimeOmega[#]==2&] (* Harvey P. Dale, Feb 15 2018 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Aug 31 2006
EXTENSIONS
a(31)-a(103) from Robert G. Wilson v, Mar 16 2009
STATUS
approved