1326

Number

$1326$ (one thousand, three hundred and twenty-six) is:

$2 \times 13 \times 51$

The $5$th hexamorphic number after $1$, $45$, $66$, $1225$:

$1326 = H_{26}$

The $26$th hexagonal number after $1$, $6$, $15$, $28$, $45$, $66$, $91$, $\ldots$, $703$, $780$, $861$, $946$, $1035$, $1128$, $1225$:

$1326 = \ds \sum_{k \mathop = 1}^{26} \paren {4 k - 3} = 26 \paren {2 \times 26 - 1}$

The $51$st triangular number after $1$, $3$, $6$, $10$, $15$, $\ldots$, $990$, $1035$, $1081$, $1128$, $1176$, $1225$, $1275$:

$1326 = \ds \sum_{k \mathop = 1}^{51} k = \dfrac {51 \times \paren {51 + 1} } 2$