Higher = more secure but slower. 2^14 recommended for interactive logins, 2^20 for file encryption.
Scrypt is a password-based key derivation function designed to be computationally intensive and memory-hard, making it resistant to hardware brute-force attacks. It was created by Colin Percival in 2009 and is used in various cryptocurrencies including Litecoin. The main parameters are N (CPU/memory cost), r (block size), and p (parallelization).