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A350409
Primes p such that 2*p+1 has exactly three prime factors (not necessarily distinct).
1
13, 31, 37, 73, 97, 103, 127, 137, 139, 181, 193, 199, 211, 227, 241, 269, 277, 307, 313, 331, 373, 379, 397, 433, 457, 463, 467, 541, 547, 563, 571, 587, 617, 619, 647, 709, 727, 733, 739, 751, 757, 773, 797, 829, 859, 883, 887, 929, 977, 1021, 1033, 1069, 1117, 1123
OFFSET
1,1
LINKS
EXAMPLE
For p = 31, 2*p+1 = 63, which factors as 3*3*7.
For p = 97, 2*p+1 = 195, which factors as 3*5*13.
MAPLE
filter:= proc(p) isprime(p) and numtheory:-bigomega(2*p+1)=3 end proc:
select(filter, [seq(i, i=3..2000, 2)]); # Robert Israel, Nov 09 2022
MATHEMATICA
Select[Prime@Range@200, PrimeOmega[2#+1]==3&] (* Giorgos Kalogeropoulos, Jan 08 2022 *)
PROG
(PARI) is(n) = bigomega(2*n + 1) == 3 && isprime(n) \\ David A. Corneth, Jan 06 2022
CROSSREFS
Sequence in context: A023274 A349636 A129864 * A080387 A348300 A100589
KEYWORD
nonn,easy
AUTHOR
Paul Duckett, Jan 06 2022
EXTENSIONS
More terms from David A. Corneth, Jan 06 2022
STATUS
approved