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A242272
Numbers n such that n*9^n+1 is semiprime.
1
1, 8, 12, 16, 20, 50, 208, 254, 282, 342, 350, 386
OFFSET
1,2
COMMENTS
The semiprimes of this form are: 10, 344373769, 3389154437773, 29648323021629457, 243153309181138576021, ...
a(13) >= 512. - Hugo Pfoertner, Aug 05 2019
MATHEMATICA
Select[Range[70], PrimeOmega[# 9^# + 1] == 2 &]
PROG
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [1..70] | IsSemiprime(s) where s is n*9^n+1];
CROSSREFS
Cf. similar sequences listed in A242203.
Cf. A064747.
Sequence in context: A192544 A302139 A160392 * A078609 A084809 A186407
KEYWORD
nonn,more,hard
AUTHOR
Vincenzo Librandi, May 10 2014
EXTENSIONS
a(7)-a(12) from Hugo Pfoertner, Aug 05 2019
STATUS
approved