OFFSET
1,1
COMMENTS
Cf. A063643 Primes p such that p +- 2 are semiprimes.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
29 - 4 = 25 = 5*5 (semiprime). 29 + 4 = 33 = 3*11 (semiprime).
MATHEMATICA
fQ[n_] := Plus @@ Last /@ FactorInteger@n == 2; Select[ Prime@ Range[3, 345], fQ[ # - 4] && fQ[ # + 4] &] (* Robert G. Wilson v, May 01 2006 *)
Select[Prime[Range[400]], PrimeOmega[#-4]==PrimeOmega[#+4]==2&] (* Harvey P. Dale, Oct 15 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Mar 08 2006
STATUS
approved