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Triangle numbers are $0,1,3,6,10...$ And square numbers are $0,1,4,9,16...$ $N$'th triangle no. = $N(N+1)/2$ $N$'th square no. = $N\cdot N$

So I was wondering are there any numbers which are in both these lists apart from $0,1$??

I found one using trial and error that is $36$ which is the $8$'th triangular number and $6$'th square number. Are there more? What is the algebraic method to calculate them?? thanks in advance.


marked as duplicate by Stella Biderman, Lord Shark the Unknown, Nosrati, Chris Godsil, Shailesh Dec 17 '17 at 3:13

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