"Deuteronomy 16:9-10 Seven sevens shall thou number unto thee: begin to number the seven sevens from such time as thou begin to put the sickle to the corn. And thou shalt keep the feast of sevens unto the LORD thy God with a tribute of a freewill offering of  thine hand, which thou shalt give unto the LORD thy God, according as the LORD thy God hath blessed thee" (DLT: torahtimes.org).

sevens: The Hebrew word  שבעת is plural derivative of שבע, the word for "seven".  The text sums up two different ways of counting the "sevens".   First seven Sabbaths are counted after Passover in the period of 49 days following the 15th of Nisan (Lev. 23:11, 15).  In that case, a "seven" would be the seventh day.  In fact, one might interpret the text as "seven sevenths", i.e. Sabbaths, since in Hebrew the cardinal number may be used with an ordinal meaning.   A like method of counting is used in Daniel 9:24-27, where "sevens" are "sevenths", i.e. the Sabbatical year. (cf. Deut. 15:9).  A second method of counting is to count periods of seven days seven times.  "Seven sevens" of days are counted so that the total number of days is 49.   These "sevens" are not regular weeks, but broken weeks.  At the end of the 49th day is the feast of Shavuot, also called the 50th day.   These two countings are a result of the history of the Exodus and the giving of the ten words.   The counting of Sabbaths and seven day periods begins on the 16th of Nisan, which was a Sabbath that year.  The seventh Sabbath was on Iyyar 28, and after it days, 44, 45, 46, 47, 48, and 49 are counted, completing the seven sevens of days.  This takes us to the end of Sivan 5, which was a Friday that year.   Then at sunset God spoke the ten commandments to Israel, which was the start of the 50th day.  The next morning on the Sabbath day, they kept a feast, and the 70 elders of Israel went up on Mt. Sinai to see God.   So the whole method of counting is to serve as a reminder of the historical events.  From the 16th of Nisan, when they camped outside Egypt the first time till the 5th of Sivan was exactly 49 days, a period enclosing exactly seven Sabbaths.   Amazingly this chronology agrees exactly with the received Jewish tradition in Seder Olam as to the week days of the events, and also with astronomical retro-calculation of the very days themselves. (DLC: torahtimes.org)

Daniel's Literal Translation and Commentary: (http://www.torahtimes.org/translation/deu1609.html)