DOC: Fix math expression

Add omited {} to math expressions
[skip ci]

Author: bashtage

randomstate/shims/pcg-32/pcg-32.pxi

@@ -41,8 +41,8 @@ RandomState(seed=None)
 Container for the PCG-32 pseudo random number generator.
 
 PCG-32 is a 64-bit implementation of O'Neill's permutation congruential 
-generator ([1]_, [2]_). PCG-32 has a period of :math:`2^64` and supports advancing
-an arbitrary number of steps as well as :math:`2^63` streams.
+generator ([1]_, [2]_). PCG-32 has a period of :math:`2^{64}` and supports advancing
+an arbitrary number of steps as well as :math:`2^{63}` streams.
 
 ``pcg32.RandomState`` exposes a number of methods for generating random
 numbers drawn from a variety of probability distributions. In addition to the

randomstate/shims/pcg-64/pcg-64-docstring.pxi

@@ -4,8 +4,8 @@ RandomState(seed=None)
 Container for the PCG-64 pseudo random number generator.
 
 PCG-64 is a 128-bit implementation of O'Neill's permutation congruential
-generator ([1]_, [2]_). PCG-64 has a period of :math:`2^128` and supports advancing
-an arbitrary number of steps as well as :math:`2^127` streams.
+generator ([1]_, [2]_). PCG-64 has a period of :math:`2^{128}` and supports advancing
+an arbitrary number of steps as well as :math:`2^{127}` streams.
 
 ``pcg64.RandomState`` exposes a number of methods for generating random
 numbers drawn from a variety of probability distributions. In addition to the

randomstate/shims/xorshift1024/xorshift1024.pxi

@@ -50,8 +50,8 @@ RandomState(seed=None)
 Container for the xorshift1024* pseudo random number generator.
 
 xorshift1024* is a 64-bit implementation of Saito and Matsumoto's XSadd
-generator [1]_. xorshift1024* has a period of :math:`2^1024 - 1` and
-supports jumping the sequence in increments of :math:`2^512`, which allow multiple
+generator [1]_. xorshift1024* has a period of :math:`2^{1024} - 1` and
+supports jumping the sequence in increments of :math:`2^{512}`, which allow multiple
 non-overlapping sequences to be generated.
 
 ``xorshift1024.RandomState`` exposes a number of methods for generating random

randomstate/shims/xorshift128/xorshift128.pxi

@@ -45,8 +45,8 @@ RandomState(seed=None)
 Container for the xorshift128+ pseudo random number generator.
 
 xorshift128+ is a 64-bit implementation of Saito and Matsumoto's XSadd
-generator [1]_. xorshift128+ has a period of :math:`2^128 - 1` and
-supports jumping the sequence in increments of :math:`2^64`, which allow multiple
+generator [1]_. xorshift128+ has a period of :math:`2^{128} - 1` and
+supports jumping the sequence in increments of :math:`2^{64}`, which allow multiple
 non-overlapping sequences to be generated.
 
 ``xorshift128.RandomState`` exposes a number of methods for generating random
@@ -78,7 +78,7 @@ seed : {None, int}, optional
 Notes
 -----
 See xorshift1024 for an implementation with a larger period
-:math:`2^1024 - 1` and jump size.
+(:math:`2^{1024} - 1`) and jump size (:math:`2^{512} - 1`).
 
 **Parallel Features**