A280643 - OEIS

%I #9 Oct 06 2023 11:00:16

%S 29,34,39,46,118,125,141,142,155,161,170,211,213,477,489,511,522,526,

%T 529,535,554,573,582,586,589,631,632,633,645,663,680,691,699,723,733,

%U 744,747,770,785,790,816,817,832,854,859,863,869,873,878,892,897,901,923

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

%C The sequence of cubes starts: 24389, 39304, 59319, 97336, 1643032, 1953125, 2803221, 2863288, ...

%H Lars Blomberg, <a href="/A280643/b280643.txt">Table of n, a(n) for n = 1..10000</a>

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

%e 29^3 = 24(3)89, 161^3 = 417(3)281, 663^3 = 2914(3)4247.

%t Select[Range[925],OddQ[len=Length[IntegerDigits[#^3]]]&&Part[IntegerDigits[#^3],(len+1)/2]==3 &] (* _Stefano Spezia_, Oct 03 2023 *)

%Y Cf. A280640-A280642, A280644-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