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A351872
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Numbers k such that either k-1 or k/2 is prime, but not both.
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0
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3, 8, 10, 12, 18, 20, 22, 24, 26, 30, 32, 34, 42, 44, 46, 48, 54, 58, 60, 68, 72, 80, 82, 84, 86, 90, 94, 98, 102, 104, 106, 108, 110, 114, 118, 122, 128, 132, 134, 138, 140, 142, 146, 150, 152, 164, 166, 168, 174, 178, 180, 182, 192, 198, 200, 202, 206, 212, 214, 218, 224, 226
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OFFSET
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1,1
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COMMENTS
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Numbers k with exactly 1 divisor d such that k-d is prime.
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LINKS
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MATHEMATICA
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Select[Range[250], Xor @@ PrimeQ[{#-1, #/2}] &] (* Amiram Eldar, Feb 23 2022 *)
Select[Range[250], Total[Boole[PrimeQ[{#-1, #/2}]]]==1&] (* Harvey P. Dale, Nov 05 2023 *)
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PROG
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(PARI) isok(k) = bitxor(isprime(k-1), !(k%2) && isprime(k/2)); \\ Michel Marcus, Feb 23 2022
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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