Triangular Number Pairs with Triangular Sum and Difference/Examples/T39, T44/Mistake

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): $780$