A050688 - OEIS

%I #31 Sep 04 2021 10:09:10

%S 8,9,15,17,18,26,27,35,36,44,45,53,54,56,62,63,71,72,80,81,89,90,98,

%T 99,107,108,109

%N Numbers k such that A000422(k) is nonsquarefree.

%H Patrick De Geest, <a href="http://www.worldofnumbers.com/revfact.htm">Reversed Smarandache Concatenated Numbers, Prime factors from n down to 1</a>

%H M. Fleuren, <a href="http://www.gallup.unm.edu/~smarandache/michafleuren.htm">Factors and primes of Smarandache sequences</a>.

%H M. Fleuren, <a href="http://www.gallup.unm.edu/~smarandache/micha.txt">Smarandache Factors and Reverse factors</a>

%H Carlos Rivera, <a href="http://www.primepuzzles.net/puzzles/puzz_008.htm">Puzzle 8. Primes by Listing</a>, The Prime Puzzles & Problems Connection.

%e a(2)=9 because 987654321 = 3^2 * 17^2 * 379721.

%Y Cf. A013929, A000422, A048288, A048342, A050687, A050675.

%K nonn,base,hard

%O 1,1

%A _Patrick De Geest_, Aug 15 1999

%E Definition corrected by _Charles R Greathouse IV_, Sep 20 2012

%E a(17)-a(24) and name corrected by _Sean A. Irvine_, Aug 17 2021

%E a(25)-a(27) from _Daniel Suteu_, Aug 18 2021