The On-Line Encyclopedia of Integer Sequences (OEIS)

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A117328

Primes p such that p +- 4 are semiprimes.
(history; published version)

#9 by Harvey P. Dale at Sun Oct 15 13:29:28 EDT 2017

STATUS

editing

approved

#8 by Harvey P. Dale at Sun Oct 15 13:29:23 EDT 2017

LINKS

Harvey P. Dale, <a href="/A117328/b117328.txt">Table of n, a(n) for n = 1..1000</a>

MATHEMATICA

Select[Prime[Range[400]], PrimeOmega[#-4]==PrimeOmega[#+4]==2&] (* Harvey P. Dale, Oct 15 2017 *)

STATUS

approved

editing

#7 by Jon E. Schoenfield at Fri Jul 31 20:52:51 EDT 2015

STATUS

editing

approved

#6 by Jon E. Schoenfield at Fri Jul 31 20:52:48 EDT 2015

NAME

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

COMMENTS

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

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] &] (from _* _Robert G. Wilson v_, May 01 2006 *)

STATUS

approved

editing

#5 by Charles R Greathouse IV at Sat Jul 14 11:41:08 EDT 2012

MATHEMATICA

fQ[n_] := Plus @@ Last /@ FactorInteger@n == 2; Select[ Prime@ Range[3, 345], fQ[ # - 4] && fQ[ # + 4] &] (from _Robert G. Wilson v (rgwv(at)rgwv.com), _, May 01 2006)

Discussion

Sat Jul 14

11:41

OEIS Server: https://oeis.org/edit/global/1816

#4 by Russ Cox at Fri Mar 30 17:26:21 EDT 2012

AUTHOR

_Zak Seidov (zakseidov(AT)yahoo.com), _, Mar 08 2006

Discussion

Fri Mar 30

17:26

OEIS Server: https://oeis.org/edit/global/139

#3 by N. J. A. Sloane at Mon Oct 09 03:00:00 EDT 2006

MATHEMATICA

fQ[n_] := Plus @@ Last /@ FactorInteger@n == 2; Select[ Prime@ Range[3, 345], fQ[ # - 4] && fQ[ # + 4] &] (from RGWv Robert G. Wilson v (rgwv(at)rgwv.com), May 01 2006)

KEYWORD

nonn,new

nonn

#2 by N. J. A. Sloane at Fri May 19 03:00:00 EDT 2006

MATHEMATICA

fQ[n_] := Plus @@ Last /@ FactorInteger@n == 2; Select[ Prime@ Range[3, 345], fQ[ # - 4] && fQ[ # + 4] &] (from RGWv (rgwv(at)rgwv.com), May 01 2006)

KEYWORD

nonn,new

nonn

#1 by N. J. A. Sloane at Fri Feb 24 03:00:00 EST 2006

NAME

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

DATA

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

1,1

COMMENTS

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

EXAMPLE

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

CROSSREFS

Cf. A063643.

KEYWORD

nonn

AUTHOR

Zak Seidov (zakseidov(AT)yahoo.com), Mar 08 2006

STATUS

approved