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A328058 Primes p such that 2*p-1 is a semiprime. 1
5, 11, 13, 17, 29, 43, 47, 61, 67, 71, 73, 89, 101, 103, 107, 109, 127, 151, 181, 191, 197, 223, 227, 241, 251, 269, 277, 283, 317, 349, 359, 373, 397, 409, 421, 433, 457, 461, 467, 487, 521, 541, 569, 571, 631, 643, 647, 659, 673, 701, 709, 719, 733, 739, 751, 757, 769, 821, 857, 859, 881, 883 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
a(3)=13 is in the sequence because it is prime and 2*13-1=5^2 is a semiprime.
MAPLE
select(t -> isprime(t) and numtheory:-bigomega(2*t-1)=2, [2, seq(i, i=3..10000, 2)]);
MATHEMATICA
Select[Prime@ Range@ 153, PrimeOmega[2 # - 1] == 2 &] (* Michael De Vlieger, Oct 03 2019 *)
PROG
(Magma) [p: p in PrimesUpTo(1000)| &+[d[2]: d in Factorization(2*p-1)] eq 2]; // Marius A. Burtea, Oct 03 2019
(PARI) isok(p) = isprime(p) && (bigomega(2*p-1) == 2); \\ Michel Marcus, Oct 04 2019
CROSSREFS
Cf. A000040, A001358. Includes A067756 and A162336.
Sequence in context: A230288 A124662 A226614 * A191042 A049511 A024900
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Oct 03 2019
STATUS
approved

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Last modified April 23 06:58 EDT 2024. Contains 371906 sequences. (Running on oeis4.)