61,728,399,382,716

Number
$61 \, 728 \, 399 \, 382 \, 716$ is:


 * $2^2 \times 3^2 \times 11 \times 73 \times 101 \times 137 \times 154 \, 321$


 * The $11 \, 111 \, 111$th triangular number:
 * $61 \, 728 \, 399 \, 382 \, 716 = \dfrac {11 \, 111 \, 111 \times \left({11 \, 111 \, 111 + 1}\right)} 2$


 * The $12$th palindromic triangular number after $0$, $1$, $3$, $6$, $66$, $3003$, $66 \, 066$, $617 \, 716$, $3 \, 544 \, 453$, $6 \, 172 \, 882 \, 716$, $30 \, 416 \, 261 \, 403$ whose index is itself palindromic:
 * $61 \, 728 \, 399 \, 382 \, 716 = T_{11 \, 111 \, 111}$