OFFSET
1,1
LINKS
P. De Geest, Repunits prime factors
Makoto Kamada, Factorizations of 11...11 (Repunit)
Eric Weisstein's World of Mathematics, Repunit
MATHEMATICA
Select[Range[350], PrimeOmega[FromDigits[PadRight[{}, #, 1]]]==4&] (* Harvey P. Dale, Oct 27 2020 *)
PROG
(PARI) isok(n) = bigomega((10^n - 1)/9) == 4; \\ Michel Marcus, Apr 23 2017
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Patrick De Geest, Jul 15 1998
EXTENSIONS
More terms from Robert Gerbicz, Nov 22 2010
Offset corrected to 1, a(18)-a(20) added by Ray Chandler, Apr 23 2017
STATUS
approved