diff --git a/notebooks/problem0021.ipynb b/notebooks/problem0021.ipynb
index 86888f6..4abf6ca 100644
--- a/notebooks/problem0021.ipynb
+++ b/notebooks/problem0021.ipynb
@@ -92,31 +92,13 @@
     "        yield dsum[n]"
    ]
   },
-  {
-   "cell_type": "markdown",
-   "id": "fdbabc18",
-   "metadata": {},
-   "source": [
-    "Here's a check to make sure the sieve matches the values from SageMath."
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 3,
-   "id": "0539d1fc",
-   "metadata": {},
-   "outputs": [],
-   "source": [
-    "s = list(sum_of_divisors_sieve(10000))\n",
-    "assert all(s[n] == sigma(n) for n in range(1, 10000))"
-   ]
-  },
   {
    "cell_type": "markdown",
    "id": "a847f754",
    "metadata": {},
    "source": [
     "## Relevant sequences\n",
+    "* Sums of divisors: [A000203](https://oeis.org/A000203)\n",
     "* Amicable numbers: [A063990](https://oeis.org/A063990)"
    ]
   }
diff --git a/notebooks/problem0023.ipynb b/notebooks/problem0023.ipynb
index 04f4486..c0ddcbe 100644
--- a/notebooks/problem0023.ipynb
+++ b/notebooks/problem0023.ipynb
@@ -63,6 +63,7 @@
    "metadata": {},
    "source": [
     "## Relevant sequences\n",
+    "* Sums of divisors: [A000203](https://oeis.org/A000203)\n",
     "* Numbers that are not the sum of two abundant numbers: [A048242](https://oeis.org/A048242)"
    ]
   }