OFFSET
1,1
COMMENTS
a(10) >= 217. - Hugo Pfoertner, Aug 06 2019
574 and 601 are also terms in this sequence. - Kevin P. Thompson, May 02 2022
LINKS
factordb.com, Status of 10^217+217.
EXAMPLE
3 is in this sequence because 10^3+3 = 17*59 is semiprime.
7 is in this sequence because 10^7+7 = 941*10627 and these two factors are prime.
MATHEMATICA
Select[Range[70], PrimeOmega[10^# + #]==2 &]
PROG
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..70] | IsSemiprime(s) where s is 10^m+m];
(PARI) is(n)=bigomega(10^n + n)==2 \\ Anders Hellström, Aug 15 2015
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Vincenzo Librandi, Dec 27 2014
EXTENSIONS
a(8) from Carl Schildkraut, Aug 15 2015
Missing a(8) term added by Kevin P. Thompson, May 02 2022
STATUS
approved