Now age 85, he continues to spread his enthusiasm for mathematics and numbers and ... “I’m still looking for all kinds of large prime numbers that are easy to remember,” Gupta says.

Remember when 100 seemed like such a huge number? When we're new to maths, we don't always understand how big numbers can get. Have some fun thinking about large, gigantic numbers with this maths ...

Microsoft Excel is a powerful spreadsheet program that can be used for a variety of tasks, including basic math. Here's how .