OFFSET
1,4
LINKS
T. D. Noe, Table of n, a(n) for n=1..1000
EXAMPLE
a(4)=2 because between prime(4)=7 and prime(5)=11 there are two semiprimes: 3*3 and 2*5.
a(11)=3 because between p(11)=31 and p(12)=37 there are three semiprimes: 33=3*11, 34=2*17 and 35=5*7.
MATHEMATICA
fQ[n_] := Plus @@ Last /@ FactorInteger[n] == 2; f[n_] := Count[fQ /@ Range[Prime[n] + 1, Prime[n + 1] - 1], True]; Table[ f[n], {n, 105}] (* Robert G. Wilson v, May 07 2005 *)
Table[Count[Range[Prime[n], Prime[n+1]], _?(PrimeOmega[#]==2&)], {n, 110}] (* Harvey P. Dale, Sep 29 2019 *)
CROSSREFS
The first occurrence of k = 0, 1, 2, ... is at position 1, 2, 4, 11, 24, 34, 30, 47, ... (A103669).
KEYWORD
base,nonn
AUTHOR
Zak Seidov, Feb 12 2005
STATUS
approved