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A046415 Repunit of length a(n) has exactly 4 prime factors (counted with multiplicity). 0
8, 9, 10, 14, 41, 43, 49, 53, 109, 157, 167, 173, 197, 199, 223, 229, 269, 283, 307, 349 (list; graph; refs; listen; history; text; internal format)
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

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: A154967 A271211 A072381 * A091417 A069237 A070480

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

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Last modified June 17 15:23 EDT 2019. Contains 324186 sequences. (Running on oeis4.)