A046414 Repunit of length a(n) has exactly 3 prime factors (counted with multiplicity).

13, 31, 37, 38, 67, 73, 83, 97, 101, 103, 113, 127, 149, 163, 191, 227, 241, 263, 313, 331, 373, 379

Offset

1,1

Comments

467 <= a(23) <= 857. 857, 1303, 1483, 2267 are terms of this sequence. - Chai Wah Wu, Nov 03 2019

Links

Table of n, a(n) for n=1..22.

P. De Geest, Repunits prime factors

Makoto Kamada, Factorizations of 11...11 (Repunit)

Eric Weisstein's World of Mathematics, Repunit

Example

a(n)=13 so 1111111111111 = 53*79*265371653.

Prog

(PARI) is(n)=bigomega(10^n\9)==3 \\ Charles R Greathouse IV, Mar 11 2014

Crossrefs

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

Sequence in context: A299130 A156532 A227435 * A023694 A038465 A103665

Adjacent sequences: A046411 A046412 A046413 * A046415 A046416 A046417

Keyword

nonn,more,base

Author

Patrick De Geest, Jul 15 1998

Extensions

More terms from Robert Gerbicz, Nov 22 2010

More terms from Bo Gyu Jeong, Jun 12 2012

Status

approved