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A117328 Primes p such that p +- 4 are semiprimes. 5
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
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
Cf. A063643.
Sequence in context: A042947 A134555 A164075 * A274227 A230027 A105406
KEYWORD
nonn
AUTHOR
Zak Seidov, Mar 08 2006
STATUS
approved

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Last modified March 29 00:26 EDT 2024. Contains 371264 sequences. (Running on oeis4.)