Cho các số: 1;2;4;6;7;8;9;21;23. Các số nguyên tố trong các số đó là

\[\left\{ {1\,;\,\,2\,;\,\,4\,;\,\,6\,;\,\,7\,;\,\,8\,;\,\,9\,;\,\,21\,;\,\,23} \right\}\].

\[\left\{ {2\,;\,\,7\,;\,\,9\,;\,\,21\,;\,\,23} \right\}\].

\[\{ 1\,;\,\,2\,;\,\,7\,;\,\,21\,;\,\,23\} \].

\[\{ 2\,;\,\,7\,;\,\,23\} \].