The Instant Math Puzzle

4+4+1+1+4+4+1+1+4+4+1+1+4+4+1+1+4+4+1+1
How many minutes did it take for you to decode the pattern and find the answer? May not be very difficult for a grown up. But, this was a math problem given for me by my little genius. How did he even think of one such puzzle. That's a bit long story.
Winding back the clock to Friday. We were in the car; it was a two day trip visiting Navagraha Temples around the religious town, Kumbakonam. For the past one year, our car journey's are always peaceful. With the little one enjoying his rear seat driving set up (he has a mock set-up with a steering wheel, gear box and an ABC control). He keeps an eye on the road, keenly observes his dad, changes the gear as he does, monitors the speed of the car and virtually drives his car; meanwhile mom and dad would be peacefully enjoying the journey. Occasionally when he gets bored I try to engage him by playing word games or some math puzzles (he loves'em). On that day, as Prajwal was driving his mock car he asked "Amma, shall we play math game?". I was feeling extremely sleepy (I slept less than 3 hours the previous night, we stayed at my friends' place that night, it was a catch up after 15 years and we kept talking until 2.30 am) and hence asked him if we can do only one for now; he agreed and gave me the above problem 🤨. My instant reaction was 😯. I asked him if he can repeat it once again assuming he was trying to give me a random puzzle, but I was awestruck when he uttered the answer before stating the puzzle again. Now, I concentrated on the problem and found out it has a pattern. How can a seven year old come up with such a puzzle on the spot? After answering to his question I inquired him. He pointed to a bus in front of us. It had the text "Blow Horn". It's 4+4 letters and the vehicle number started in "1" series. That's how he had framed it. Way too smart I would say 😍