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A252657
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Numbers m such that 4^m - m is a semiprime.
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2
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OFFSET
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1,1
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COMMENTS
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549, 721, and 755 are in the sequence, but not necessarily the next three terms. The other possibilities for a(9) are 483, 503, and 543. - Robert Israel, Feb 10 2019
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LINKS
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EXAMPLE
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2 is in this sequence because 4^2-2 = 2*7 is semiprime.
17 is in this sequence because 4^17-17 = 6971*2464477 and these two factors are prime.
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MATHEMATICA
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Select[Range[120], PrimeOmega[4^# - #]==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 [2..120] | IsSemiprime(s) where s is 4^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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