2601

Number
$2601$ (two thousand, six hundred and one) is:


 * $3^2 \times 17^2$


 * The $51$st square number after $1, 4, 9, 16, 25, 36, \ldots, 1521, 1600, 1681, 1764, 1936, 2025, 2116, 2209, 2304, 2401, 2500$:
 * $2601 = 51 \times 51$


 * The $17$th pentagonal pyramidal number after $1, 6, 12, 40, 75, 126, 196, 288, 405, 550, 726, 936, 1183, 1470, 1800, 2176$:
 * $2601 = \displaystyle \sum_{k \mathop = 1}^{17} \dfrac {k \left({3 k - 1}\right)} 2 = \dfrac {17^2 \left({17 + 1}\right)} 2$