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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The semiprimes of this form are: 9, 129, 1537, 1207959553, 113336795588871485128705, 2535301200456458802993406410753, ...

a(15) >= 483. - Hugo Pfoertner, Aug 05 2019

LINKS

Table of n, a(n) for n=1..14.

factordb.com, Status of 483*8^483+1.

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.

Cf. A064746, A242178.

Sequence in context: A274495 A299705 A318231 * A056198 A143742 A038523

Adjacent sequences:  A242268 A242269 A242270 * A242272 A242273 A242274

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

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Last modified May 6 18:38 EDT 2021. Contains 343586 sequences. (Running on oeis4.)