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%I A046412 #37 Feb 16 2025 08:32:39
%S A046412 9,18,22,27,36,42,44,45,54,63,66,72,78,81,84,88,90,99,108,110,111,117,
%T A046412 126,132,135,144,153,154,156,162,168,171,176,180,189,198,205,207,210,
%U A046412 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 A046412 Lengths of nonsquarefree repunits.
%C A046412 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 A046412 P. De Geest, <a href="/load/view.php?a=aHR0cHM6Ly93d3cud29ybGRvZm51bWJlcnMuY29tL3JlcHVuaXRzLmh0bQ">Repunits prime factors</a>
%H A046412 Eric Weisstein's World of Mathematics, <a href="/load/view.php?a=aHR0cHM6Ly9tYXRod29ybGQud29sZnJhbS5jb20vUmVwdW5pdC5odG1s">Repunit</a>
%F A046412 a(n)=k where (10^k-1)/9 is not squarefree. - _Ray Chandler_, Aug 10 2003
%p A046412 remove(t -> numtheory:-issqrfree((10^t-1)/9), [$1..90]); # _Robert Israel_, Dec 30 2015
%t A046412 Select[Range[300],!SquareFreeQ[(10^#-1)/9]&] (* _Harvey P. Dale_, Jun 26 2013 *)
%o A046412 (PARI) isok(n) = ! issquarefree((10^n-1)/9); \\ _Michel Marcus_, Dec 31 2015
%Y A046412 Cf. A000042, A004022, A046053, A084006, A087094.
%K A046412 nonn,base
%O A046412 1,1
%A A046412 _Patrick De Geest_, Jul 15 1998
%E A046412 Terms to a(60) from _Ray Chandler_, Aug 10 2003
%E A046412 a(61)-a(67) from _Max Alekseyev_, Apr 29 2022

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