For example, 2x 3-8 decoders allows you to build a 4 - 16 decoder. 4x 3-8 decoders, allows you yo build a 5 - 32 decoder. 8x 3-8 decoders, allows you to build a 6-64 decoder, and so on.
2 decods. = 4 bits input.
4 decods. = 5 bits input.
8 decods. = 6 bits input.
16 decods. = 7 bits input.
You have a sequence there. For 13 bits input you need 1024 decoders.