diff --git a/doc/source/notebooks/tour_of_pygam.ipynb b/doc/source/notebooks/tour_of_pygam.ipynb
index d4d89f30..0768ab93 100644
--- a/doc/source/notebooks/tour_of_pygam.ipynb
+++ b/doc/source/notebooks/tour_of_pygam.ipynb
@@ -11,7 +11,7 @@
     "Generalized Additive Models (GAMs) are smooth semi-parametric models of the form:\n",
     "\n",
     "$$\n",
-    "    g(\\mathbb{E}[y|X]) = \\beta_0 + f_1(X_1) + f_2(X_2, X3) + \\ldots + f_M(X_N)\n",
+    "    g(\\mathbb{E}[y|X]) = \\beta_0 + f_1(X_1) + f_2(X_2, X_3) + \\ldots + f_M(X_N)\n",
     "$$\n",
     "\n",
     "where `X.T = [X_1, X_2, ..., X_N]` are independent variables, `y` is the dependent variable, and `g()` is the link function that relates our predictor variables to the expected value of the dependent variable.\n",
@@ -44,14 +44,14 @@
     "\n",
     "where \n",
     "$$\n",
-    "g(\\mu|X) = \\beta_0 + f_1(X_1) + f_2(X_2, X3) + \\ldots + f_M(X_N)\n",
+    "g(\\mu|X) = \\beta_0 + f_1(X_1) + f_2(X_2, X_3) + \\ldots + f_M(X_N)\n",
     "$$\n",
     "\n",
     "So we can see that a GAM has 3 components:\n",
     "\n",
     "- ``distribution`` from the exponential family\n",
     "- ``link function`` $g(\\cdot)$\n",
-    "- ``functional form`` with an additive structure $\\beta_0 + f_1(X_1) + f_2(X_2, X3) + \\ldots + f_M(X_N)$\n",
+    "- ``functional form`` with an additive structure $\\beta_0 + f_1(X_1) + f_2(X_2, X_3) + \\ldots + f_M(X_N)$\n",
     "\n",
     "### Distribution: \n",
     "Specified via: ``GAM(distribution='...')``\n",