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A289250 Primes p such that p + 4 is a semiprime. 2
2, 5, 11, 17, 29, 31, 47, 53, 61, 73, 83, 89, 107, 137, 139, 151, 157, 173, 179, 181, 197, 199, 211, 233, 263, 283, 317, 331, 337, 367, 373, 389, 409, 433, 443, 449, 467, 523, 541, 547, 569, 577, 587, 593, 607, 619, 631, 677, 683, 691, 709, 719, 727, 733, 751, 787, 809, 811, 827 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Except for case p=5, p+4 is never a perfect square.
For p = {2, 11, 31, 73, 139, 433, 1759, 2017} p+4 is a product of two consecutive primes.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
2+4=6=2*3, 5+4=9=3*3, 11+4=15=3*5 (all semiprimes).
MATHEMATICA
Select[Prime@ Range@ 150, PrimeOmega[# + 4] == 2 &] (* Michael De Vlieger, Jun 29 2017 *)
PROG
(PARI) issemi(n)=bigomega(n)==2
is(n)=isprime(n) && issemi(n+4) \\ Charles R Greathouse IV, Jul 02 2017
CROSSREFS
Sequence in context: A048210 A153222 A023222 * A278049 A007491 A124850
KEYWORD
nonn
AUTHOR
Zak Seidov, Jun 29 2017
STATUS
approved

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Last modified May 21 17:21 EDT 2024. Contains 372738 sequences. (Running on oeis4.)