设数列 $\left\{ {a_n} \right\}$:\[1, - 2, - 2,3,3,3, - 4, - 4, - 4, - 4, \cdots ,\underbrace {{{\left( { - 1} \right)}^{k - 1}}k, \cdots ,{{\left( { - 1} \right)}^{k - 1}}k}_{k~\text{个}}, \cdots ,\]即当 $\dfrac{{\left( {k - 1} \right)k}}{2} < n \leqslant \dfrac{{k\left( {k + 1} \right)}}{2}$($k \in {{\mathbb{N}}^{\ast}}$)时,${a_n} = {\left( { - 1} \right)^{k - 1}}k$.记 ${S_n} = {a_1} + {a_2} + \cdots + {a_n}$($n \in {{\mathbb{N}}^{\ast}}$).对于 $l \in {{\mathbb{N}}^{\ast}}$,定义集合 ${P_l} = \left\{ {n\mid {S_n}~\text{是}~{a_n}~\text{的整数倍}~,n \in {{\mathbb{N}}^{\ast}},~\text{且}~1 \leqslant n \leqslant l} \right\}$.
1、求集合 ${P_{11}}$ 中元素的个数.
2、求集合 ${P_{2000}}$ 中元素的个数.
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