Was the year 1976 a leap year?

No

1975 wasn't a leap year, but if it was a leap year however, it would've been a double leap year lasting 367 days. The reason for this being is because the length of year is not 365-1/4 days or 365.25 days or 365 days and 6 hours. It's because the length of year is 365.24 days, 365-1/5 days + 1/25 days which adds up to 365-6/25 days which means we normally should only have 6 leap years in 25 years. That's where 6/25 comes from.

We can have leap years in years divisible by 5 and double leap years in years divisible by 25. However, the length of year is just a tidbit longer than 365-6/25 days and is inbetween 365-6/25 and 365-1/4 days so we could also add a triple leap year every 475 years to smooth things out and have stand alone triple leap years inbetween. The length of year is longer than 365-23/95 days or 365.2421 days approximately, but if the length of the year shortens by then, we wouldn't need these extra triple leap years because it won't accumulate by a full day anymore.

We have leap years per every fourth year to make things easier. You'll need a special program if you want to make your leap years your own way.