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A046412 Lengths of nonsquarefree repunits. 5

%I #35 Apr 29 2022 20:21:19

%S 9,18,22,27,36,42,44,45,54,63,66,72,78,81,84,88,90,99,108,110,111,117,

%T 126,132,135,144,153,154,156,162,168,171,176,180,189,198,205,207,210,

%U 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

%N Lengths of nonsquarefree repunits.

%C 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

%H P. De Geest, <a href="http://www.worldofnumbers.com/repunits.htm">Repunits prime factors</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Repunit.html">Repunit</a>

%F a(n)=k where (10^k-1)/9 is not squarefree. - _Ray Chandler_, Aug 10 2003

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

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

%o (PARI) isok(n) = ! issquarefree((10^n-1)/9); \\ _Michel Marcus_, Dec 31 2015

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

%K nonn,base

%O 1,1

%A _Patrick De Geest_, Jul 15 1998

%E Terms to a(60) from _Ray Chandler_, Aug 10 2003

%E a(61)-a(67) from _Max Alekseyev_, Apr 29 2022

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)