Triangular Number Pairs with Triangular Sum and Difference/Examples/T39, T44/Mistake
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Source Work
1986: David Wells: Curious and Interesting Numbers:
- The Dictionary
- $780$
1997: David Wells: Curious and Interesting Numbers (2nd ed.):
- The Dictionary
- $780$
Mistake
- $780$ and $990$ are the $2$nd smallest pair of triangular numbers whose sum and difference ($1770$ and $210$) are also triangular.
It is in fact the $4$th such pair, not the $2$nd, after $\tuple {15, 21}$, $\tuple {105, 171}$, $\tuple {378, 703}$.
Also see
- Triangular Number Pairs with Triangular Sum and Difference/Mistake, where the source of the error is explained.
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $780$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $780$