http://scikit-learn.org/stable/modules/feature_extraction.html#tfidf-term-weighting

says

which would actually be 1. That however would be inconsistent with the example output (= 0 ) of the transformation above. Following the explanations above I'd say there are brackets missing around

log(6/1) + 1

Same for the next equation.