Yes, that math is correct.
Your 56gb file is only about 3% of the size of the eventual output.
There's honestly no point in generating on-disk files like these - your particular password criteria is so extremely simple to generate procedurally that any good password cracker should either have a brute force capability built in that would meet your needs, or it should be able to read wordlists from off a pipe rather than off disk.
Actually, any good password cracker should be able to do both of these things.
also, here's the math on that other guy's problem:
The password contains one digit - that's 10^1 = 10 possible combinations.
The password contains 19 lowercase alpha characters - that's 26^19 = 766467265200361890474622976 possible combinations.
If the digit was in a fixed location, then you could multiply these two numbers together and have the total number of combinations, but the digit can be anywhere in the password, so we have the following set of possibilities:
19 alphas, 1 digit
18 alphas, 1 digit, 1 alpha
17 alphas, 1 digit, 2 alphas
1 digit, 19 alphas
That's 20 possible character alignments.
The total number of password combinations is therefore 26^19 * 10^1 * 20 = 153293453040072378094924595200
Assuming that we're creating a wordlist for some program that expects each password to be delimited with a newline then that means each password is 20 bytes in size + 1 for the newline (let's ignore MSDOS/Win32 and it's CR/LF combinations).
The total storage space is therefore 26^19 * 10 * 20 * 21 = 3219162513841519939993416499200 bytes.
There's no filesystem that I know of capable of storing 2.6 million yottabytes of data, so you might be out of luck if you plan to output this data to storage.