A280645 - OEIS

%I #8 Dec 23 2024 14:53:45

%S 26,43,107,109,119,122,136,139,144,150,177,179,197,203,205,472,476,

%T 494,499,501,506,510,523,537,555,561,563,568,583,603,608,629,636,649,

%U 664,694,696,726,752,753,762,766,769,780,795,796,807,814,819,826,831,845

%N Numbers k such that k^3 has an odd number of digits and the middle digit is 5.

%C The sequence of cubes starts: 17576, 79507, 1225043, 1295029, 1685159, 1815848, 2515456, 2685619, ...

%H Lars Blomberg, <a href="/A280645/b280645.txt">Table of n, a(n) for n = 1..10000</a>

%H Jeremy Gardiner, <a href="https://web.archive.org/web/*/http://list.seqfan.eu/oldermail/seqfan/2016-December/017135.html">Middle digit in cube numbers</a>, Seqfan Mailing list, Dec 12 2016.

%e 26^3 = 17(5)76, 150^3 = 337(5)000, 603^3 = 2192(5)6227

%t Select[Range[900],OddQ[IntegerLength[#^3]]&&IntegerDigits[#^3][[(IntegerLength[ #^3]+1)/2]]==5&] (* _Harvey P. Dale_, Aug 24 2017 *)

%Y Cf. A280640-A280644, A280646-A280649, A181354.

%Y See A279420-A279429 for a k^2 version.

%Y See A279430-A279431 for a k^2 version in base 2.

%K nonn,base,easy

%O 1,1

%A _Lars Blomberg_, Jan 07 2017