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A242271
Numbers n such that n*8^n+1 is semiprime.
1
1, 2, 3, 9, 24, 32, 35, 51, 75, 234, 243, 392, 417, 472
OFFSET
1,2
COMMENTS
The semiprimes of this form are: 9, 129, 1537, 1207959553, 113336795588871485128705, 2535301200456458802993406410753, ...
a(15) >= 483. - Hugo Pfoertner, Aug 05 2019
MATHEMATICA
Select[Range[80], PrimeOmega[# 8^# + 1] == 2 &]
PROG
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [1..80] | IsSemiprime(s) where s is n*8^n+1];
CROSSREFS
Cf. similar sequences listed in A242203.
Sequence in context: A274495 A299705 A318231 * A056198 A143742 A038523
KEYWORD
nonn,more,hard
AUTHOR
Vincenzo Librandi, May 10 2014
EXTENSIONS
a(10)-a(14) from Hugo Pfoertner and Daniel Suteu, Aug 05 2019
STATUS
approved