OFFSET
1,1
COMMENTS
The semiprimes of this form are: 1535, 1572863, 1207959551, 7146825580543, 193690812773950291967, 113336795588871485128703, 2535301200456458802993406410751, 1960026433464605549549037738806984897986559, ...
MATHEMATICA
Select[Range[80], PrimeOmega[# 8^# - 1]==2&]
PROG
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [2..80] | IsSemiprime(s) where s is n*8^n-1];
(PARI) isok(n)=bigomega(n*8^n-1)==2 /* Anders Hellström, Aug 18 2015 */
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Vincenzo Librandi, May 12 2014
EXTENSIONS
a(12)-a(19) from Luke March, Aug 14 2015
STATUS
approved