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.

1, 2, 3, 9, 8, 6, 15, 12, 18, 45, 24, 32, 54, 30, 42, 64, 102, 72, 108, 154, 60, 84, 96, 140, 126, 200, 120, 204, 308, 168, 192, 280, 180, 210, 240, 252, 330

Offset

0,2

Comments

a(40) = 300; all other subsequent terms are > 322. - Ray Chandler, Apr 23 2017

a(38) = 336. - Max Alekseyev, Apr 29 2022

Links

Table of n, a(n) for n=0..36.

Prog

(PARI) a(n) = my(k=1); while(omega((10^k - 1)/9) !=n, k++); k; \\ Michel Marcus, Apr 23 2017

Crossrefs

Cf. A000042, A001221, A002275, A095370.

Sequence in context: A021421 A152812 A246825 * A008291 A261525 A122665

Adjacent sequences: A086562 A086563 A086564 * A086566 A086567 A086568

Keyword

more,nonn

Author

Amarnath Murthy, Aug 31 2003

Extensions

Corrected and extended by Sascha Kurz, Sep 22 2003

a(12)-a(15) from David Wasserman, Mar 28 2005

a(16)-a(27) from Donovan Johnson, Nov 17 2008

a(28)-a(35) from Ray Chandler, Apr 23 2017

a(36) from Max Alekseyev, Apr 29 2022

Status

approved