I'm on mobile so sorry if spoiler text doest work...

>!First I wondered if it was maths related, like adding for subtracting a series of numbers, but the two fives and eights kinda ruined any progressions.

I looked at if the numbers stood for the months, or days or letters in the alphabet but no dice.

Then I thought that the first 3 could stand for 'the', and tried make a sentence like 'the number that comes...', but realised the gradually increasing numbers of letters probably meant there was a numerical element.

Then I kinda but both methods together and realised that 2-3-4 had 4-5-4 letters respectively, and then once I realised the third in sequence was actually 5 and not 4 it made sense.!<