The mathematical conundrum

I came across this mathematical conundrum this evening. I discussed it with a friend who knows his way around an N sequence and we've disagreed on the answer. In short, his is 6, mine is 9. He was N^2 - N (yes, exactly), mine was each figure on the left is multiplied by 7, 6, 5, 4 in descending order.

The mathematical conundrum is not just literal, but goes deeper on a personal level. My great uncle Bill was a math genius - I only met him once as he lived most of his life in Minnesota and Arizona, and he gave me a book. His book. To a ten year-old kid this was amazing - my uncle wrote an actual book. The book is available on Amazon, and it's entitled 'The place of the circle in elemental geometry'. I went onto be in the top percentile in the country for 4th year high school arithmetic. Now here's the conundrum. I went from that, and with a great uncle the author of a book whose very title would confuse some, to less than 30% for 5th year maths. In sum (see what I did there?) it went bad when geometry went all cos, sin and tan. Maybe I got the math genes from somewhere else, maybe I loss interest because as I predicted at 16, I would never again use cos, sin and tan. It was a sign, and that sign was not mathematical.