How does Hannah\Chaya remember her number?

"J for Jew. And 1 for me, alone. I am very, very much alone. And 9...in English it is pronounced 'nine', which is like the German word for no. No, I will not die here...Seven is for...each and every day of the week I stay alive. One day at a time. Then 2 for Gitl and Shmuel, who are here in this place, too...And 4 is for my family, I think. I almost remember them. If I close my eyes they are there, hovering within sight. But when I open my eyes, they are gone" (Chapter 14).

Each digit on her arm stands for something that has meaning to her.