diff --git a/exercises/luhn/example.R b/exercises/luhn/example.R
index b0d063e5..c676b56e 100644
--- a/exercises/luhn/example.R
+++ b/exercises/luhn/example.R
@@ -1,35 +1,23 @@
-# Convert a number to a valid number, if it isn't already.
-luhn <- function(input) {
-  if (is_valid(input)) {
-    return(input)
-  }
-  diff <- (10 - checksum(10*input)) %% 10
-  return(10 * input + diff)
-}
-
-# Get the check digit
-check_digit <- function(input) {
-  as.numeric(substring(input,nchar(input))) 
-}
-
-# Compute the checksum
-checksum <- function(input) {
-  sum(addends(input))
-}
-
 # Determine whether the number is valid.
 is_valid <- function(input) {
-  checksum(input) %% 10 == 0
-}
-
-# addends returns the vector of numbers that follow the luhn algorithm
-addends <- function(input) {
-  check <- check_digit(input)
-  v <- as.numeric(strsplit(as.character(input),"")[[1]])
-  # counting from right double value of every second digit
-  start_seq <- ifelse(length(v) %% 2 == 1, 0, 1)
-  v2 <- replace(v,seq(start_seq,length(v),2),v[seq(start_seq,length(v),2)]*2)
-  v2 <- ifelse(v2 > 9, v2 - 9, v2)
-  replace_vals <- v2[seq(start_seq,length(v),2)]
-  replace(v,seq(start_seq,length(v),2),replace_vals)
+  
+  # Strip spaces, check length & check for invalid characters
+  input_vector <- strsplit(gsub(pattern = " ", replacement = "", input), "")[[1]]
+  if (length(input_vector) < 2 || any(grepl("[^[:digit:]]", input_vector))) {
+    return (FALSE)
+  }
+  
+  # Convert to numeric
+  num_vector <- as.numeric(input_vector)
+  
+  # Double every second digit starting from the right
+  num_vector <- rev(num_vector)
+  num_vector[seq(2,length(num_vector),2)] = num_vector[seq(2,length(num_vector),2)]*2
+  
+  # Subtract 9 if > 9 (can apply to all since no digit can be greater than 9 before doubling)
+  num_vector <- ifelse(num_vector > 9, num_vector - 9, num_vector)
+  
+  # Check checksum is divisible by 10
+  sum(num_vector) %% 10 == 0
+  
 }
diff --git a/exercises/luhn/luhn.R b/exercises/luhn/luhn.R
index 3db9494f..fd2e1384 100644
--- a/exercises/luhn/luhn.R
+++ b/exercises/luhn/luhn.R
@@ -1,25 +1,4 @@
-# Convert a number to a valid number, if it isn't already.
-luhn <- function() {
-
-}
-
-# Get the check digit
-check_digit <- function() {
-
-}
-
-# Compute the checksum
-checksum <- function() {
-
-}
-
 # Determine whether the number is valid.
-is_valid <- function() {
+is_valid <- function(input) {
 
 }
-
-
-# addends returns the vector of numbers that follow the luhn algorithm
-addends <- function(input) {
-
-}
\ No newline at end of file
diff --git a/exercises/luhn/test_luhn.R b/exercises/luhn/test_luhn.R
index 25906de3..e6a7614d 100644
--- a/exercises/luhn/test_luhn.R
+++ b/exercises/luhn/test_luhn.R
@@ -1,81 +1,69 @@
-source('./luhn.R')
+source('./is_valid.R')
 suppressPackageStartupMessages({ require(testthat) })
 
-test_that("check digit", {
-  input <- 34567
-  expect_equal(check_digit(input),
-    7
-  )
+test_that("single digit strings can not be valid", {
+  input <- "1"
+  expect_equal(is_valid(input), FALSE)
 })
 
-test_that("check digit with input ending in zero", {
-  input <- 91370
-  expect_equal(check_digit(input),
-    0
-  )
+test_that("A single zero is invalid", {
+  input <- "0"
+  expect_equal(is_valid(input), FALSE)
 })
 
-test_that("check addends", {
-  input <- 12121
-  expect_equal(addends(input),
-    c(1,4,1,4,1)
-  )
+test_that("simple valid sin", {
+  input <- " 5 9 "
+  expect_equal(is_valid(input), TRUE)
 })
 
-test_that("check too large addends", {
-  input <- 8631
-  expect_equal(addends(input),
-    c(7,6,6,1)
-  )
+test_that("valid Canadian SIN", {
+  input <- "046 454 286"
+  expect_equal(is_valid(input), TRUE)
 })
 
-test_that("checksum", {
-  input <- 4913
-  expect_equal(checksum(input),
-    22
-  )
+test_that("invalid Canadian SIN", {
+  input <- "046 454 287"
+  expect_equal(is_valid(input), FALSE)
 })
 
-test_that("checksum of larger number", {
-  input <- 201773
-  expect_equal(checksum(input),
-    21
-  )
+test_that("invalid credit card", {
+  input <- "8273 1232 7352 0569"
+  expect_equal(is_valid(input), FALSE)
 })
 
-test_that("check invalid number", {
-  input <- 738
-  expect_equal(is_valid(input),
-    FALSE
-  )
+test_that("valid strings with a non-digit added become invalid", {
+  input <- "046a 454 286"
+  expect_equal(is_valid(input), FALSE)
 })
 
-test_that("check valid number", {
-  input <- 8739567
-  expect_equal(is_valid(input),
-    TRUE
-  )
+test_that("punctuation is not allowed", {
+  input <- "055-444-285"
+  expect_equal(is_valid(input), FALSE)
 })
 
-test_that("create valid number", {
-  input <- 123
-  expect_equal(luhn(input),
-    1230
-  )
+test_that("symbols are not allowed", {
+  input <- "055£ 444$ 285"
+  expect_equal(is_valid(input), FALSE)
 })
 
-test_that("create larger valid number", {
-  input <- 873956
-  expect_equal(luhn(input),
-    8739567
-  )
+test_that("single zero with space is invalid", {
+  input <- " 0"
+  expect_equal(is_valid(input), FALSE)
 })
 
-test_that("create even larger valid number", {
-  input <- 837263756
-  expect_equal(luhn(input),
-    8372637564
-  )
+test_that("lots of zeros are valid", {
+  input <- " 00000"
+  expect_equal(is_valid(input), TRUE)
+})
+
+test_that("another valid sin", {
+  input <- "055 444 285"
+  expect_equal(is_valid(input), TRUE)
+})
+
+test_that("nine doubled is nine", {
+  input <- "091"
+  expect_equal(is_valid(input), TRUE)
 })
 
 print("All tests passed!")