Integer is Sum of Three Triangular Numbers/Historical Note

Historical Note on Integer is Sum of Three Triangular Numbers

Carl Friedrich Gauss proved that every Integer is Sum of Three Triangular Numbers.

The $18$th entry in his diary, dated $10$th July $1796$, made when he was $19$ years old, reads:

$**\Epsilon\Upsilon\Rho\Eta\Kappa\Alpha \quad \text{num} = \Delta + \Delta + \Delta.$

Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $3$
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $3$