OFFSET
1,1
COMMENTS
Semiprime analog of A031131 "Difference between n-th prime and (n+2)nd prime."
EXAMPLE
a(1) = 5 because 3rd semiprime - first semiprime = 9 - 4 = 5.
a(2) = 4 because semiprime(4) - semiprime(2) = 10 - 6 = 4.
a(3) = 5 because semiprime(5) - semiprime(3) = 14 - 9 = 5.
a(4) = 5 because semiprime(6) - semiprime(4) = 15 - 10 = 5.
MATHEMATICA
t = Select[ Range@320, Plus @@ Last /@ FactorInteger@# == 2 &]; Drop[t, 2] - Drop[t, -2] (* Robert G. Wilson v *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Jan 20 2006
EXTENSIONS
More terms from Robert G. Wilson v, Jan 21 2006
STATUS
approved