diff --git a/notebooks/problem0026.ipynb b/notebooks/problem0026.ipynb
index e9f4cee..20a8808 100644
--- a/notebooks/problem0026.ipynb
+++ b/notebooks/problem0026.ipynb
@@ -40,7 +40,7 @@
     "\n",
     "If $d = 2^a 5^b n$ where $n$ is coprime to 2 and 5, then the [period](https://mathworld.wolfram.com/DecimalPeriod.html) of $\\frac{1}{d}$ is the [multiplicative order](https://en.wikipedia.org/wiki/Multiplicative_order) of 10 modulo $n$. This is the same as finding the smallest positive $k$ such that\n",
     "$$10^k \\equiv 1 \\pmod{n}$$\n",
-    "(Wondering why this is called multiplicative order? It has to do with the mathematical concept of [groups](https://en.wikipedia.org/wiki/Group_(mathematics)), but you don't need to be familiar with them to apply the formula.)\n",
+    "(Wondering why this is called multiplicative order? It has to do with the mathematical concept of [groups](https://w.wiki/NeN), but you don't need to be familiar with them to apply the formula.)\n",
     "\n",
     "Based on the definition, we can easily write a function that computes multiplicative order that is efficient enough for this problem, but it's not very efficient in general. The computation is a special case of the [discrete logarithm](https://en.wikipedia.org/wiki/Discrete_logarithm), which has no known efficient algorithm in general."
    ]