Sunday Times Teaser 2733 – Letter Writing

by Victor Bryant

In 2014 I went to calligraphy classes that were held weekly on the same day each week in nine consecutive months.

In fact I only went to fifteen of the classes, the dates of which I wrote down in the form ‘First of January’, ‘Second of January’, …

I found that each date that I had written down used a different number of letters.

What were the dates of the first and last lessons that I attended?