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A140452
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2^(a(n))-1 contains an overpseudoprime divisor.
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1
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11, 22, 23, 25, 28, 29, 33, 35, 36, 37, 39, 41, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53, 55, 56, 57, 58, 59, 60, 63, 64, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 81, 82, 83, 84, 86, 87, 88, 90, 91, 92, 94, 95, 96, 97, 99, 100, 101, 102, 103, 104, 105, 106, 108, 109
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OFFSET
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1,1
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COMMENTS
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If p is a prime then p is in the sequence iff 2^p-1 is a composite number.
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LINKS
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PROG
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(PARI) f(n) = my(t); sumdiv(2*n+1, d, eulerphi(d)/(t=znorder(Mod(2, d))))*t-t+1; \\ A137576
isopp(n) = (n>1) && !isprime(n) && (n == f((n-1)/2)); \\ A141232
isok(n) = {fordiv(2^n-1, d, if (isopp(d), return (1)); ); return (0); } \\ Michel Marcus, Dec 09 2018
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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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