Correction: Round 20 is missing from the pdf. It should read:

I love knitting and I love puzzles, so why not combine the two?! Each puzzle piece is knit to shape, back and forth, with an invisible garter stitch seam. The pieces are joined to their neighbors with a modified running stitch. The border is two rounds of crochet slip stitch which gives the Puzzle Baby Blanket a nice rounded edge.

Description from Tangled: