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A307217
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Semiprimes p*q such that 2^(p+q) == 1 (mod p*q).
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0
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9, 15, 35, 119, 5543, 74447, 90859, 110767, 222179, 389993, 1526849, 2927297, 3626699, 4559939, 24017531, 137051711, 160832099, 229731743, 627699239, 880021141, 1001124539, 1041287603, 1104903617, 1592658611, 1717999139, 8843679683, 15575602979, 15614760199, 20374337479
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OFFSET
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1,1
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COMMENTS
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For k > 9, these are semiprimes k such that 2^(k+1) == 1 (mod k): semiprimes in A187787.
In this sequence, only 9 is a perfect square. - Jinyuan Wang, Mar 30 2019
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LINKS
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PROG
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(PARI) isok(k) = (bigomega(k)==2) && (Mod(2, k)^(k+1) == 1); \\ (for k > 9) Michel Marcus, Mar 29 2019
(Perl) use ntheory ":all"; forsemiprimes { print "$_\n" if powmod(2, vecsum(factor($_)), $_) == 1 } 4, 1e7; # Daniel Suteu, Mar 30 2019
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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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