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A259026 Numbers n such that n*23^n-1 is semiprime. 0
1, 2, 6, 8, 18, 21, 24, 26, 28, 30, 33, 230 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
After 290, which may or may not be in the sequence, 420 and 450 are definitely in the sequence.
LINKS
K. O'Bryant, Sets of Natural Numbers with Proscribed Subsets, J. Int. Seq. 18 (2015) # 15.7.7
MATHEMATICA
Select[Range[200], PrimeOmega[# 23^# - 1]==2&]
PROG
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [2..200] | IsSemiprime(s) where s is n*23^n-1];
(PARI) isok(n)=bigomega(n*23^n-1)==2 \\ Anders Hellström, Aug 20 2015
CROSSREFS
Similar sequences listed in A242273.
Sequence in context: A233572 A370864 A005823 * A178758 A024431 A152598
KEYWORD
nonn,more
AUTHOR
Luke March, Aug 06 2015
STATUS
approved

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Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)