A046415 Repunit of length a(n) has exactly 4 prime factors (counted with multiplicity).
8, 9, 10, 14, 41, 43, 49, 53, 109, 157, 167, 173, 197, 199, 223, 229, 269, 283, 307, 349
Offset: 1
Links
- P. De Geest, Repunits prime factors
- Makoto Kamada, Factorizations of 11...11 (Repunit)
- Eric Weisstein's World of Mathematics, Repunit
Programs
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Mathematica
Select[Range[350],PrimeOmega[FromDigits[PadRight[{},#,1]]]==4&] (* Harvey P. Dale, Oct 27 2020 *) -
PARI
isok(n) = bigomega((10^n - 1)/9) == 4; \\ Michel Marcus, Apr 23 2017
Extensions
More terms from Robert Gerbicz, Nov 22 2010
Offset corrected to 1, a(18)-a(20) added by Ray Chandler, Apr 23 2017