Everywhere across the west, 13 is considered to be an unlucky number. Just remember how people freak out when they hear about Friday the 13th. Yes, there are horror stories, myths, and nus that revolve around the number 13. And that is why people think 13 is an unlucky number.
However, if you shift this perspective to the east, then you will be surprised that 13 is actually considered to be lucky. Especially in countries like Thailand and India, 13 is considered to be fortunate and 13th day is considered to be a lucky day. Why?
Here are some beliefs:
In the Greek mythology, Zeus was the thirteenth, and everyone knows that Zeus was the most powerful God during the times of ancient Greece. Since then, 13 is considered to be the symbol of incorruptible, power and divinity. For them, 13 is for spiritual completion since 13 is a prime number and it can only be divided by itself, so it is a complete number in itself. Hence, it is the representation of totality, completion, and attainment.
According to Thai calendar, they celebrate their new year on 13th of April. The rituals and customs say that it is the day when the bad signs are washed away by splashing water on people.
Every month of Hindu calendar, the 13th day is an auspicious day for Hindus. The 13th day in the calendar is called Trayodashi and is dedicated to Lord Shiva. There is a belief among Hindus that if you pray to Lord Shiva, then you will be blessed with wealth, children, happiness, and prosperity. Pradosh vrat that is conducted in honour of worshipping Lord Shiva falls on 13th day of the month. Maha Shivaratri, the biggest festival dedicated to Lord Shiva, is celebrated on the 13th night in the month of Magh.
Depending on whether you are in the west or east, 13 can be either lucky or unlucky. So, just think that 13 is just a number and nothing more. There is no need to dread a number and enjoy any Friday, the 13th to its fullest.
Also, Hindus also consider looking at their birth chart to figure out their lucky numbers based on their zodiac sign.
(Reference: hinduhumanrights.info, wiki.com)