A117328 Primes p such that p +- 4 are semiprimes.

29, 53, 61, 73, 89, 137, 173, 181, 263, 331, 449, 523, 541, 547, 569, 577, 587, 593, 683, 691, 727, 811, 839, 947, 1051, 1063, 1153, 1163, 1223, 1259, 1289, 1367, 1531, 1559, 1627, 1637, 1847, 1861, 1933, 1973, 1987, 2099, 2153, 2161, 2213, 2267, 2287, 2311

Offset: 1

Author

Zak Seidov, Mar 08 2006

Keywords

• nonn

Comments

Cf. A063643 Primes p such that p +- 2 are semiprimes.

Examples

			29 - 4 = 25 = 5*5 (semiprime). 29 + 4 = 33 = 3*11 (semiprime).
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A063643.

Programs

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 *)