OFFSET
1,1
COMMENTS
LINKS
R. Zumkeller, Table of n, a(n) for n = 1..1000
EXAMPLE
a(1)=4 because 4-1 = 3 (not semiprime) and 4+1 = 5 (not semiprime).
MATHEMATICA
Mean/@SequencePosition[Table[If[PrimeOmega[n]==2, 1, 0], {n, 400}], {0, 1, 0}] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Aug 19 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Mar 25 2010
EXTENSIONS
Corrected by Reinhard Zumkeller and Ray Chandler, Apr 07 2010
STATUS
approved