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A350409
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Primes p such that 2*p+1 has exactly three prime factors (not necessarily distinct).
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1
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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
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OFFSET
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1,1
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LINKS
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EXAMPLE
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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.
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MAPLE
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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
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MATHEMATICA
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PROG
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(PARI) is(n) = bigomega(2*n + 1) == 3 && isprime(n) \\ David A. Corneth, Jan 06 2022
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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