The "P" mint mark was first used on $1 coins starting in 1979, so a 1921 silver dollar couldn't have that letter - only D or S.
In addition Philadelphia struck both Morgan and Peace dollars with that date so it's important to know which one you have. Morgan dollars have an eagle with outstretched wings on the reverse side while Peace dollars have an eagle with folded wings and the word PEACE.
There's more information at the Related Questions.
A real silver dollar has a $25.00 value just for the silver.
what is the current value of an 1878 silver dollar
Sorry no US silver dollar coins dated 1826
No US silver dollars were made after 1935, look at the back of the coin for 'Half Dollar'.
The US never printed 100 dollar silver certificates with this date.
current silver troy ounce value
Value is for the silver about $2.50
20,000
79dollars
Zero
The first US Dollar coin was struck in 1794
There was no silver dollar in the US made in 1957. It might be a half dollar. These are usually worth about $10-15.