I heard there are 620 letters in the Aseres Hadibros which corresponds to the 613 Mitzvos of the Torah and 7 Mitzvos D'Rabanan. What are the Seven Mitzvos D'Rabanan - שבע מצוות דרבנן? Is there a easy way to remember them? Is there any disagreement as to what the seven are?
The Chinuch (p394 in this edition) gives the list below and explains each in detail!
The 7 Mitzvos are:
1) Berachos - Reciting Berachos
2) Netilas Yadayim - washing your hands
3) Eruvin - allowing one to carry within an Eruv and walk further on Shabbos through an Eruv Techumin
4) Reciting Hallel on festivals
5) Ner Shabbos - Shabbos candles
6) Megilla - on Purim
7) Chanuka - lighting the Menora.
There are many mnemonics for remembering them. One from Sefer Keser Torah is:
א - אור (חנוכה) ש - שבת (נר) ר - רנה (הלל) ל - לקריאה (מגילה) ר - רחיצה (נטילת ידיים) ע - ערובין כ - כברכותיך
More can be found at wikipedia
Chasam Sofer - Parshas Yisro - Asher Lraiacha says that the seven Mitzvos are as follows.
א - Aveilus - Seven days of Aveilus
ש - Simcha - Seven days of Simchas Chasan and Kallah
ר - Rechitza - Netilas Yadayim
ל - Lechem - Not to eat Pas Akum or Bishul Akum
ר - Reshuyos - This is Eruvin which combines Reshuyos
ע - Amalaik - Reading the Megila, which goes on the eradication of haman and the people that were killed on the 13th of Adar, which were from Amalaik
כ - Kohanim - This alludes to the miracle of Chanuka which was established by the Kohanim.
I see Zvi has answered with some different Mitzvos from another reliable source, so I guess there is some disagreement as to exactly what these seven Mitzvos are.