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A242337
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Numbers k such that k*6^k - 1 is semiprime.
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1
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4, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15, 18, 22, 23, 25, 32, 35, 38, 45, 51, 54, 57, 68, 72, 82, 97, 110, 138, 155, 234, 254
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OFFSET
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1,1
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COMMENTS
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The semiprimes of this form are 5183, 38879, 279935, 1959551, 90699263, 604661759, 3990767615, 26121388031, 169789022207, 1097098297343, ...
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LINKS
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MATHEMATICA
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Select[Range[352], PrimeOmega[# 6^# - 1]==2&]
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PROG
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(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [2..352] | IsSemiprime(s) where s is n*6^n-1];
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CROSSREFS
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Cf. similar sequences listed in A242273.
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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