Given the inequality:
$$\operatorname{atan}{\left(2^{x} \right)} < 1$$
To solve this inequality, we must first solve the corresponding equation:
$$\operatorname{atan}{\left(2^{x} \right)} = 1$$
Solve:
$$x_{1} = \frac{\log{\left(\tan{\left(1 \right)} \right)}}{\log{\left(2 \right)}}$$
$$x_{1} = \frac{\log{\left(\tan{\left(1 \right)} \right)}}{\log{\left(2 \right)}}$$
This roots
$$x_{1} = \frac{\log{\left(\tan{\left(1 \right)} \right)}}{\log{\left(2 \right)}}$$
is the points with change the sign of the inequality expression.
First define with the sign to the leftmost point:
$$x_{0} < x_{1}$$
For example, let's take the point
$$x_{0} = x_{1} - \frac{1}{10}$$
=
$$- \frac{1}{10} + \frac{\log{\left(\tan{\left(1 \right)} \right)}}{\log{\left(2 \right)}}$$
=
$$- \frac{1}{10} + \frac{\log{\left(\tan{\left(1 \right)} \right)}}{\log{\left(2 \right)}}$$
substitute to the expression
$$\operatorname{atan}{\left(2^{x} \right)} < 1$$
$$\operatorname{atan}{\left(2^{- \frac{1}{10} + \frac{\log{\left(\tan{\left(1 \right)} \right)}}{\log{\left(2 \right)}}} \right)} < 1$$
/ 1 log(tan(1))\
| - -- + -----------|
| 10 log(2) | < 1
atan\2 /
the solution of our inequality is:
$$x < \frac{\log{\left(\tan{\left(1 \right)} \right)}}{\log{\left(2 \right)}}$$
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