A328058 Primes p such that 2*p-1 is a semiprime.
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
Offset: 1
Keywords
Examples
a(3)=13 is in the sequence because it is prime and 2*13-1=5^2 is a semiprime.
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Programs
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Magma
[p: p in PrimesUpTo(1000)| &+[d[2]: d in Factorization(2*p-1)] eq 2]; // Marius A. Burtea, Oct 03 2019
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Maple
select(t -> isprime(t) and numtheory:-bigomega(2*t-1)=2, [2,seq(i,i=3..10000,2)]);
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Mathematica
Select[Prime@ Range@ 153, PrimeOmega[2 # - 1] == 2 &] (* Michael De Vlieger, Oct 03 2019 *)
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PARI
isok(p) = isprime(p) && (bigomega(2*p-1) == 2); \\ Michel Marcus, Oct 04 2019