cp's OEIS Frontend

A086565 Smallest k such that (10^k - 1)/9 has n distinct prime divisors. Or a(n)= smallest value of k such that A000042(k) has exactly n distinct prime divisors.

%I A086565 #18 Apr 29 2022 23:31:23
%S A086565 1,2,3,9,8,6,15,12,18,45,24,32,54,30,42,64,102,72,108,154,60,84,96,
%T A086565 140,126,200,120,204,308,168,192,280,180,210,240,252,330
%N A086565 Smallest k such that (10^k - 1)/9 has n distinct prime divisors. Or a(n)= smallest value of k such that A000042(k) has exactly n distinct prime divisors.
%C A086565 a(40) = 300; all other subsequent terms are > 322. - _Ray Chandler_, Apr 23 2017
%C A086565 a(38) = 336. - _Max Alekseyev_, Apr 29 2022
%o A086565 (PARI) a(n) = my(k=1); while(omega((10^k - 1)/9) !=n, k++); k; \\ _Michel Marcus_, Apr 23 2017
%Y A086565 Cf. A000042, A001221, A002275, A095370.
%K A086565 more,nonn
%O A086565 0,2
%A A086565 _Amarnath Murthy_, Aug 31 2003
%E A086565 Corrected and extended by _Sascha Kurz_, Sep 22 2003
%E A086565 a(12)-a(15) from _David Wasserman_, Mar 28 2005
%E A086565 a(16)-a(27) from _Donovan Johnson_, Nov 17 2008
%E A086565 a(28)-a(35) from _Ray Chandler_, Apr 23 2017
%E A086565 a(36) from _Max Alekseyev_, Apr 29 2022