OFFSET
1,1
COMMENTS
The semiprimes of this form are: 161, 2186, 3188645, 344373767, 345191655698, 2701703435345984177, 14653733724766095041978322587, ...
a(15) >= 512. - Daniel Suteu, 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 [2..70] | IsSemiprime(s) where s is n*9^n-1];
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Vincenzo Librandi, May 12 2014
EXTENSIONS
a(10)-a(14) from Daniel Suteu, Aug 05 2019
STATUS
approved