A046412 Lengths of nonsquarefree repunits.

9, 18, 22, 27, 36, 42, 44, 45, 54, 63, 66, 72, 78, 81, 84, 88, 90, 99, 108, 110, 111, 117, 126, 132, 135, 144, 153, 154, 156, 162, 168, 171, 176, 180, 189, 198, 205, 207, 210, 216, 220, 222, 225, 234, 242, 243, 252, 261, 264, 270, 272, 279, 286, 288, 294, 297, 306, 308, 312, 315, 324, 330, 333, 336, 342, 351, 352

Offset

1,1

Comments

This is the set of all positive multiples of all positive members of A087094. What is the asymptotic density of this set? - Jeppe Stig Nielsen, Dec 28 2015

Links

Table of n, a(n) for n=1..67.

P. De Geest, Repunits prime factors

Eric Weisstein's World of Mathematics, Repunit

Formula

a(n)=k where (10^k-1)/9 is not squarefree. - Ray Chandler, Aug 10 2003

Maple

remove(t -> numtheory:-issqrfree((10^t-1)/9), [$1..90]); # Robert Israel, Dec 30 2015

Mathematica

Select[Range[300], !SquareFreeQ[(10^#-1)/9]&] (* Harvey P. Dale, Jun 26 2013 *)

Prog

(PARI) isok(n) = ! issquarefree((10^n-1)/9); \\ Michel Marcus, Dec 31 2015

Crossrefs

Cf. A000042, A004022, A046053, A084006, A087094.

Sequence in context: A373351 A222623 A141469 * A171081 A232056 A109661

Adjacent sequences: A046409 A046410 A046411 * A046413 A046414 A046415

Keyword

nonn,base,changed

Author

Patrick De Geest, Jul 15 1998

Extensions

Terms to a(60) from Ray Chandler, Aug 10 2003

a(61)-a(67) from Max Alekseyev, Apr 29 2022

Status

approved