I believe that pistol is from the 1965-1967 era. If you have a question please post it.
50,00,000
1.5 million is written as 1,500,000. There are six zeros in a million, so you could simply move the decimal point six places to the right. When you do that for 1.5 you will get your answer of 1,500,000.
It could be just about anything, since you are not providing many numbers. Therefore, it is hard to guess some rule. One possibility is to provide different powers of 6.
Great website to look up piano serial numbers which correspond with the year they were made: http://www.bluebookofpianos.com/serial1.htmBetween 1976-1978, probably during 1977