diff --git a/largest_product_in_a_series/largest_product_test.go b/largest_product_in_a_series/largest_product_test.go
new file mode 100644
index 0000000..26e53f8
--- /dev/null
+++ b/largest_product_in_a_series/largest_product_test.go
@@ -0,0 +1,54 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestFetchNextAdjacent(t *testing.T) {
+	tt := []struct {
+		name        string
+		wantCount   int
+		srcDigits   []int
+		wantDigits  []int
+		wantSrcLeft []int
+	}{
+		{
+			"2 out of 3",
+			2,
+			[]int{1, 2, 3},
+			[]int{2, 3},
+			[]int{},
+		},
+		{
+			"2 out of 2",
+			2,
+			[]int{1, 2},
+			[]int{},
+			[]int{1, 2},
+		},
+		{
+			"5 out of 6",
+			5,
+			[]int{1, 2, 3, 4, 5, 6},
+			[]int{2, 3, 4, 5, 6},
+			[]int{},
+		},
+		{
+			"2 out of 6",
+			2,
+			[]int{1, 2, 3, 4, 5, 6},
+			[]int{2, 3},
+			[]int{4, 5, 6},
+		},
+	}
+
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			got, got2 := FetchNextAdjacent(tc.wantCount, tc.srcDigits)
+			if !reflect.DeepEqual(got, tc.wantDigits) || !reflect.DeepEqual(got2, tc.wantSrcLeft) {
+				t.Errorf("FetchNextAdjacent(%d, %v)=%v, %v, want %v, %v", tc.wantCount, tc.srcDigits, got, got2, tc.wantDigits, tc.wantSrcLeft)
+			}
+		})
+	}
+}
diff --git a/largest_product_in_a_series/main.go b/largest_product_in_a_series/main.go
new file mode 100644
index 0000000..338ebb1
--- /dev/null
+++ b/largest_product_in_a_series/main.go
@@ -0,0 +1,66 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+var src = "73167176531330624919225119674426574742355349194934" +
+	"96983520312774506326239578318016984801869478851843" +
+	"85861560789112949495459501737958331952853208805511" +
+	"12540698747158523863050715693290963295227443043557" +
+	"66896648950445244523161731856403098711121722383113" +
+	"62229893423380308135336276614282806444486645238749" +
+	"30358907296290491560440772390713810515859307960866" +
+	"70172427121883998797908792274921901699720888093776" +
+	"65727333001053367881220235421809751254540594752243" +
+	"52584907711670556013604839586446706324415722155397" +
+	"53697817977846174064955149290862569321978468622482" +
+	"83972241375657056057490261407972968652414535100474" +
+	"82166370484403199890008895243450658541227588666881" +
+	"16427171479924442928230863465674813919123162824586" +
+	"17866458359124566529476545682848912883142607690042" +
+	"24219022671055626321111109370544217506941658960408" +
+	"07198403850962455444362981230987879927244284909188" +
+	"84580156166097919133875499200524063689912560717606" +
+	"05886116467109405077541002256983155200055935729725" +
+	"71636269561882670428252483600823257530420752963450"
+
+func main() {
+	var nextSrc []int
+	for len(src) > 0 {
+		i, err := strconv.Atoi(src[0:1])
+		if err != nil {
+			panic(err)
+		}
+		nextSrc = append(nextSrc, i)
+		src = src[1:]
+	}
+	var next []int
+	var out int
+	for {
+		next, nextSrc = FetchNextAdjacent(13, nextSrc)
+		if len(next) == 0 {
+			break
+		}
+		var product = next[0:1][0]
+		next = next[1:]
+		for _, v := range next {
+			product = product * v
+		}
+		if product > out {
+			out = product
+		}
+	}
+
+	fmt.Println("the largest product is", out)
+}
+
+func FetchNextAdjacent(n int, src []int) ([]int, []int) {
+	if n >= len(src) {
+		return []int{}, src
+	}
+	ret := make([]int, n)
+	copy(ret, src[1:n+1])
+	return ret, src[n+1:]
+}