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::It needs a source, but the RHS is obviously just the Cartesian product of two isosceles right triangles 0≤x≤y≤N and 0≤z≤w≤N in the xy and zw planes, a natural geometric interpretation of a squared triangular number. —[[User:David Eppstein|David Eppstein]] ([[User talk:David Eppstein|talk]]) 07:01, 16 February 2021 (UTC)
:::Thank you for this explanation; it's a lot clearer than the paragraph in the article itself. Perhaps you'd like to improve that paragraph - or at least give it a tag that you feel is more appropriate than "Confusing"? [[User:PatricKiwi|PatricKiwi]] ([[User talk:PatricKiwi|talk]]) 07:28, 16 February 2021 (UTC)
==Triangular numbers of squares==
I recently added that these numbers are the alternating sums of Triangular numbers of squares, similar to how triangular numbers are the alternating sums of squares, however this was removed because of a lack of proof:
0+1 is 1
1+9 is 10 ( triangle 4)
9+36 is 45 (triangle 9)
36+100 is 136 (triangle 16)
100+225 is 325 (triangle 25)
225+441 is 666 (triangle 36)
441+784 is 1225 (triangle 49)
784+1296 is 2080 (triangle 64)
1296+2025 is 3321 (triangle 81)
2025+3025 is 5050 (triangle 100) [[User:KlokkoVanDenBerg|KlokkoVanDenBerg]] ([[User talk:KlokkoVanDenBerg|talk]]) 09:29, 7 April 2022 (UTC)
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