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A242205
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Numbers n such that n*5^n+1 is semiprime.
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1
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OFFSET
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1,2
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COMMENTS
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The semiprimes of this form are 6, 51, 2501, 2441406250001, 10013580322265626, 363797880709171295166015625001, ...
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LINKS
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MATHEMATICA
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Select[Range[90], PrimeOmega[# 5^# + 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 [1..90] | IsSemiprime(s) where s is n*5^n+1];
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CROSSREFS
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Cf. similar sequences listed in A242203.
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KEYWORD
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nonn,more,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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