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

1,1

Links

Table of n, a(n) for n=1..20.

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

Cf. A000042, A001222, A002275, A004022, A004023, A046053.

Sequence in context: A271211 A341044 A072381 * A358674 A358675 A091417

Adjacent sequences: A046412 A046413 A046414 * A046416 A046417 A046418

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