Definition: In this task, you will use your knowledge about language (and common sense) to determine what element the marked number refers to. The numbers are marked with two underlines around them, like: _ number _. Your answer should be chosen from the given text, and should not contain other words.
Input: Howard Wolowitz:  Wha the hell is _ 43 _ ?
Raj Koothrappali: It 's a prime number . Encryption systems are based on prime numbers .
Howard Wolowitz: What kind of secrets would Sheldon need encrypting ?
Raj Koothrappali: Maybe it 's the secret to what makes his egg salad so delicious .
Howard Wolowitz: It 's paprika .
Raj Koothrappali: Really ? Well , one mystery solved .

number