title: Hexagonal Number
signature: hexagonalNumber :: Integer -> Integer
  hexagonalNumber n = 
test_code: import Text.Printf
  import Control.Exception (catch, SomeException)
  import Data.Typeable
  import qualified Data.List as List
  import qualified Data.Map as Map
  import qualified Data.Set as Set
  
  -- SOLUTION CODE
  -- ============================================
  
  PLACEHOLDER_CODE_BODY
  
  -- TESTING CODE 
  -- ============================================
  validateSolution :: Integer -> Integer -> Bool
  validateSolution actual expected = do
      actual == expected
  
  
  driver :: Integer -> Integer -> String
  driver n expected = do
      if (validateSolution (PLACEHOLDER_FN_NAME n) expected)
          then "PASSED"
      else "FAILED"
  
  main = do
      printf "TEST-0...%s\n" (driver (38) (2850) )
  
      printf "TEST-1...%s\n" (driver (44) (3828) )
  
      printf "TEST-2...%s\n" (driver (58) (6670) )
  
      printf "TEST-3...%s\n" (driver (10) (190) )
  
      printf "TEST-4...%s\n" (driver (31) (1891) )
  
      printf "TEST-5...%s\n" (driver (53) (5565) )
  
      printf "TEST-6...%s\n" (driver (94) (17578) )
  
      printf "TEST-7...%s\n" (driver (64) (8128) )
  
      printf "TEST-8...%s\n" (driver (71) (10011) )
  
      printf "TEST-9...%s\n" (driver (59) (6903) )
  
source_py: def hexagonal_number(n):
      return (n * ((2 * n) - 1))
source_cpp: int hexagonal_number(int n) {
    return n * ( 2 * n - 1 );
  }