clear all; close all; clc

a = [0 0 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 0 0;
      11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020]';

%  GESUCHTE AUSGABE
%  a = [0 0 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 0 0];

largeEnough = a >= 3;
smallEnough = a <= 18;

% [r, c, v] = find(largeEnough & smallEnough);
% a(1:r-1, 1) = 0;
% a(r(end)+1:a(end)) = 0;

a = nonzeros(a);