A117328 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

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 *)