diff --git a/2020/15.py b/2020/15.py
new file mode 100755
index 0000000..e88f3d2
--- /dev/null
+++ b/2020/15.py
@@ -0,0 +1,90 @@
+#!/usr/bin/env python
+
+from aoc import get_input # AoC
+from collections import defaultdict
+
+nums = list(map( int, get_input(15).split(",")))
+
+firstNums = defaultdict(list)
+
+i = 0
+for n in nums:
+    firstNums[n].append(i)
+    i += 1
+
+
+def addSeen(num):
+    firstNums.add(num)
+
+def copyNums(lst):
+    return [elem for elem in lst]
+
+def getFirstNum(num, start=len(firstNums)):
+    i = start
+    while i >= 0:
+        n = firstNums[i]
+        if( n[0] == num ):
+            return n[1]
+        i -= 1
+
+
+# def getNextNum(i):
+#     if( i >= len(nums) ):
+#         lastNum = nums[i-1]
+#         newNums = nums[:i-1]
+
+#         if( lastNum == nums[i-2] ):
+#             nums.append(1)
+#             addSeen(1)
+
+#         elif( not lastNum in firstNums ): # new number
+#             nums.append(0)
+#             addSeen( (lastNum, i-1) )
+
+#         elif( lastNum in firstNums ): # spoken before
+#             ei= getFirstNum(lastNum)
+#             fi = getFirstNum(lastNum, ei-1)
+#             newN = ei - fi # diff is still the same if ei = ei+1
+#             nums.append(newN)
+#             addSeen( (newN, i-1) )
+
+
+# turn = 3
+
+# while True:
+#     if( turn < 30000000 ):
+#         getNextNum(turn)
+#         print(turn, "/30000000")
+#         turn += 1
+#     else:
+#         print(nums[-1])
+#         break
+
+
+
+
+def numbers(maxt):
+    num = nums[-1]
+    prevnum = None
+    for i in range(len(nums), maxt):
+        numsSeen = len(firstNums[num])
+
+        if( numsSeen > 1 ):
+            num = firstNums[num][-1] - firstNums[num][-2]
+        else:
+            num = 0
+
+        print(f"{num=} {i=} {nums=}")
+        firstNums[num].append(i)
+
+    return num
+
+
+
+
+turn = 3
+#maxturn = 30000000
+#maxturn = 2020
+maxturn = 10
+print("0, 3, 6, 0, 3, 3, 1, 0, 4, 0")
+print(numbers(maxturn))