diff --git a/.gitignore b/.gitignore
index 16bdf0e..43950d6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,5 @@
 .DS_Store
 
 c/binaries
+*/bin/*
+*.dwarf
diff --git a/crystal/001/euler001 b/crystal/001/euler001
deleted file mode 100755
index c08b083..0000000
Binary files a/crystal/001/euler001 and /dev/null differ
diff --git a/crystal/001/euler001.dwarf b/crystal/001/euler001.dwarf
deleted file mode 100644
index bb4d2a3..0000000
Binary files a/crystal/001/euler001.dwarf and /dev/null differ
diff --git a/crystal/002/euler002 b/crystal/002/euler002
deleted file mode 100755
index 1a6705c..0000000
Binary files a/crystal/002/euler002 and /dev/null differ
diff --git a/crystal/002/euler002.dwarf b/crystal/002/euler002.dwarf
deleted file mode 100644
index 88fe852..0000000
Binary files a/crystal/002/euler002.dwarf and /dev/null differ
diff --git a/crystal/003/euler003 b/crystal/003/euler003
deleted file mode 100755
index 963c05e..0000000
Binary files a/crystal/003/euler003 and /dev/null differ
diff --git a/crystal/003/euler003.cr b/crystal/003/euler003.cr
deleted file mode 100644
index 38be85b..0000000
--- a/crystal/003/euler003.cr
+++ /dev/null
@@ -1,26 +0,0 @@
-#wrong approach, should just do recursive trial division...
-
-def eratosthenes_sieve(n)
-  sieve = Array.new(n + 1, true)
-  sieve[0] = false
-  sieve[1] = false
-
-  2.step(to: Math.sqrt(n)) do |i|
-    if sieve[i]
-      (i * i).step(to: n, by: i) do |j|
-        sieve[j] = false
-      end
-    end
-  end
-
-  result = sieve.map_with_index { |b, i| b ? i : nil }.compact
-end
-
-def prime_factors(n)
-  nums = eratosthenes_sieve(n).select { |i| n % i == 0 }
-  nums = nums + nums.map { |i| n / i }
-end
-
-puts eratosthenes_sieve(600851475143)
-
-puts prime_factors(600851475143).max
diff --git a/crystal/003/euler003.dwarf b/crystal/003/euler003.dwarf
deleted file mode 100644
index 07ba194..0000000
Binary files a/crystal/003/euler003.dwarf and /dev/null differ
diff --git a/crystal/euler.cr b/crystal/euler.cr
new file mode 100644
index 0000000..17dcdce
--- /dev/null
+++ b/crystal/euler.cr
@@ -0,0 +1,23 @@
+# miscellaneous stuff
+
+module Euler
+  def self.eratosthenes_sieve(n)
+    sieve = Array.new(n + 1, true)
+    sieve[0] = false
+    sieve[1] = false
+
+    2.step(to: Math.sqrt(n)) do |i|
+      if sieve[i]
+        (i * i).step(to: n, by: i) do |j|
+          sieve[j] = false
+        end
+      end
+    end
+
+    result = sieve.map_with_index { |b, i| b ? i : nil }.compact
+  end
+
+  def self.palindrome?(x)
+    x.to_s.reverse == x.to_s
+  end
+end
diff --git a/crystal/001/euler001.cr b/crystal/euler001.cr
similarity index 100%
rename from crystal/001/euler001.cr
rename to crystal/euler001.cr
diff --git a/crystal/002/euler002.cr b/crystal/euler002.cr
similarity index 100%
rename from crystal/002/euler002.cr
rename to crystal/euler002.cr
diff --git a/crystal/euler003.cr b/crystal/euler003.cr
new file mode 100644
index 0000000..cd5ab03
--- /dev/null
+++ b/crystal/euler003.cr
@@ -0,0 +1,27 @@
+alias NumType = Int32 | Int64 | UInt32 | UInt64
+
+def trial_division(n : NumType)
+  factors = [] of NumType
+  check = ->(p: NumType) {
+    q, r = n.divmod(p)
+    while r.zero?
+      factors << p
+      n = q
+      q, r = n.divmod(p)
+    end
+  }
+
+  check.call(2)
+  check.call(3)
+  p = 5
+  while p * p <= n
+    check.call(p)
+    p += 2
+    check.call(p)
+    p += 4
+  end
+  factors << n if n > 1
+  factors
+end
+
+puts trial_division(600851475143).max
diff --git a/crystal/euler004.cr b/crystal/euler004.cr
new file mode 100644
index 0000000..6b9b4e6
--- /dev/null
+++ b/crystal/euler004.cr
@@ -0,0 +1,7 @@
+require "./euler"
+
+def products_of_three_digit_nums
+  (100..999).to_a.combinations(2).map { |p| p.product }
+end
+
+puts products_of_three_digit_nums.select { |x| Euler.palindrome?(x) }.max