DouKaku?

function n = finddoubleinb13(rmax)
% Returns a sequence of digits that is twice bigger in base 13 than in base 10.
% The numbers from 10 to rmax in base 10 will be checked (ja.doukaku.org Q14).
n10 = (10:rmax)';
n13 = base2dec(num2str(n10),13);
idx = find(~mod(n13(:),n10(:)));
n = min(n10(idx));
% plot(n10,n13(:)./n10(:))
% grid on