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A169643
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Numbers n such that neither composite(n)-+1 is composite.
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1
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1, 2, 6, 10, 19, 28, 42, 51, 75, 79, 104, 114, 138, 148, 152, 178, 187, 212, 221, 247, 278, 338, 348, 372, 423, 465, 490, 504, 525, 539, 669, 679, 683, 709, 729, 848, 858, 873, 883, 909, 961, 1028, 1071, 1080, 1089, 1104, 1202, 1221, 1247, 1251, 1354, 1363
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OFFSET
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1,2
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COMMENTS
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LINKS
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EXAMPLE
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a(1)=1 because composite(1)-1=3=prime and composite(1)+1=5=prime.
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MATHEMATICA
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Position[Select[Range[2000], CompositeQ], _?(AllTrue[#+{1, -1}, PrimeQ]&), 1, Heads->False]// Flatten (* Harvey P. Dale, Jan 16 2024 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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