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A252658
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Numbers m such that 5^m - m is a semiprime.
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2
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1, 3, 8, 14, 18, 48, 52, 54, 62, 72, 96, 98, 114, 186, 486, 524, 712
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OFFSET
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1,2
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COMMENTS
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There are no other known terms under 1000 - the only possible terms are 812 and 908. - Carl Schildkraut, Aug 21 2015
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LINKS
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EXAMPLE
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1 is in this sequence because 5^1-1 = 2*2 is semiprime.
18 is in this sequence because 5^18-18 = 199*19169332993 and these two factors are prime.
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MATHEMATICA
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Select[Range[100], PrimeOmega[5^# - #]==2 &]
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PROG
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(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..100] | IsSemiprime(s) where s is 5^m-m];
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CROSSREFS
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Cf. similar sequences listed in A252656.
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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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