I have a little obsession with prime numbers, so this app is great fun for me. Back in high school (in 1975) I was in the first computer programming class in the LAUSD. I wrote a little program to give me a list of prime numbers. The program would be run, at night, on the school districts IBM 360, and took forever (many minutes) just to calculate a number as small 103. This app handles much much larger numbers with ease, in fractions of a second. I love it!