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%I #42 Aug 24 2020 23:08:11
%S 12,30,40
%N Numbers k such that there are no palindromic triangular numbers of length k.
%H P. De Geest, <a href="http://www.worldofnumbers.com/square.htm">Palindromic Squares</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/PalindromicNumber.html">Palindromic Number</a>
%t A003098 = Select[PolygonalNumber[3, Range[0, 10^6]], PalindromeQ];
%t (* Set Range to level of desired running time. *)
%t nopal[n_] := Length[Select[A003098, IntegerLength[#] == n || (n == 1 && # == 0) &]]; Select[Range[12], nopal[#] == 0 &]
%t (* Set Range to encompass length of last value in A003098. *)
%Y Cf. A000217, A003098, A008509, A034822.
%K nonn,base,hard,more
%O 1,1
%A _Robert Price_, May 01 2019
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