[Home] [Puzzles & Projects] [Delphi Techniques] [Math topics] [Library] [Utilities]
|
|
Problem Description
A fifth entry in our "Numeric T-Shirt" line: Back of T-Shirt: "The smallest 3-digit emirp!" Front: __ __ __ ? Background & TechniquesA "emirp" is a prime number which forms a different prime number when its digits are reversed. (Palindromic primes are excluded by this definition.) Not much new work here - we borrowed the IsPrime and Reverse functions from T-Shirt #4 . So all that is left for the SearchBtnClick method is to run through a loop looking for primes, checking if the reverse is a prime, and checking that they are not the same. If a number that meets these three conditions, add it to a display list. I added a TUpDown box to select how many digits, N, in the emirps of interest. A 3-line IntPower function lets us set the lower limit of our search as 10(N-1) and the upper limit at one less than 10 times the lower limit. For 3-digit emirps for example, that means that at most we'll search from 10(3-1) = 102 = 100 up to 10×100-1=1000-1=999. That pretty much covers the 3-digit candidates. We search for emirps up to 9 digits, so we'll limit the display to 100 hits - we really don't need thousands (or millions) of them displayed. About 50 lines of code here, well within the beginner's range. Running/Exploring the Program
Suggestions for Further Explorations
|
[Feedback] [Newsletters (subscribe/view)] [About me]Copyright © 2000-2018, Gary Darby All rights reserved. |