21 Number game in Python (original) (raw)

Last Updated : 17 Jan, 2026

21 Number Game (also known as Bagram or Twenty Plus One) is a simple counting game in which players take turns to count numbers from 1 to 21. The player who calls "21" loses the game. It can be played between multiple players, but here we demonstrate a player vs computer version using Python. For Example:

Player says: 1 2
Computer says: 3 4 5
Player says: 6 7
Computer says: 8 9
...
Player says: 21

Since the Player says 21, the Player loses the game.

Game Rules

The game is played between two players who take turns one after another.
On each turn, a player can call 1 to 3 numbers.
The numbers must be consecutive (for example, 5 6 7) skipping numbers leads to disqualification.
The counting always starts from 1 and continues upward.
The one who calls 21, loses the game.

Python Implementation

Below is the Python program that implements the 21 Number Game with a player vs computer strategy.

Python `

def nearestMultiple(num): if num >= 4: near = num + (4 - (num % 4)) else: near = 4 return near

def lose1(): print("\n\nYOU LOSE!") print("Better luck next time!") exit(0)

def check(xyz): i = 1 while i < len(xyz): if (xyz[i] - xyz[i-1]) != 1: return False i += 1 return True

def start1(): xyz = [] last = 0 while True: print("Enter 'F' to take the first chance.") print("Enter 'S' to take the second chance.") chance = input('> ')

    if chance.upper() == "F":
        while True:
            if last == 20:
                lose1()
            print("\nYour Turn.")
            inp = int(input("How many numbers do you wish to enter? (1-3)\n> "))
            if 1 <= inp <= 3:
                comp = 4 - inp
            else:
                print("Wrong input. You are disqualified from the game.")
                lose1()

            print("Enter your numbers:")
            for _ in range(inp):
                xyz.append(int(input('> ')))

            last = xyz[-1]

            if not check(xyz):
                print("\nYou did not enter consecutive integers.")
                lose1()
            if last == 21:
                lose1()

            print("\nComputer's Turn:")
            for j in range(1, comp + 1):
                xyz.append(last + j)
            print("Numbers after computer's turn:", xyz)
            last = xyz[-1]

    elif chance.upper() == "S":
        comp = 1
        last = 0
        while last < 20:
            print("\nComputer's Turn:")
            for j in range(1, comp + 1):
                xyz.append(last + j)
            print("Numbers after computer's turn:", xyz)
            if xyz[-1] == 20:
                lose1()

            print("\nYour Turn.")
            inp = int(input("How many numbers do you wish to enter? (1-3)\n> "))
            print("Enter your numbers:")
            for _ in range(inp):
                xyz.append(int(input('> ')))
            last = xyz[-1]

            if not check(xyz):
                print("\nYou did not enter consecutive integers.")
                lose1()

            near = nearestMultiple(last)
            comp = near - last
            if comp == 4:
                comp = 3

        print("\n\nCONGRATULATIONS!!!")
        print("YOU WON!")
        exit(0)

    else:
        print("Wrong choice. Please enter F or S.")

game = True while game: print("\nPlayer 2 is Computer.") ans = input("Do you want to play the 21 number game? (Yes / No)\n> ") if ans.lower() == 'yes': start1() else: nex = input("Do you want to quit the game? (Yes / No)\n> ") if nex.lower() == "yes": print("You are quitting the game...") exit(0) elif nex.lower() == "no": print("Continuing...") else: print("Wrong choice")

**Output

Player 2 is Computer.
Do you want to start the game? (Yes/No)
> Yes
Enter 'F' to take the first chance.
Enter 'S' to take the second chance.
> S
Order of inputs after computer's turn is:
[1]

Your turn.

How many numbers do you wish to enter?
> 3
Enter your values
> 2
> 3
> 4
Order of inputs after computer's turn is:
[1, 2, 3, 4, 5, 6, 7]

Your turn.

How many numbers do you wish to enter?
> 1
Enter your values
> 8
Order of inputs after computer's turn is:
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

Your turn.

How many numbers do you wish to enter?
> 1
Enter your values
> 12
Order of inputs after computer's turn is:
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]

Your turn.

How many numbers do you wish to enter?
> 1
Enter your values
> 16
Order of inputs after computer's turn is:
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

Your turn.

How many numbers do you wish to enter?
> 1
Enter your values
> 20

CONGRATULATIONS!!!
YOU WON!

**Explanation:

nearestMultiple(num) computes the next multiple of 4 so the computer can always land on safe numbers (4, 8, 12, 16, 20).
lose1() immediately ends the program when the player reaches 21 or gives invalid input.
check(xyz) verifies that all entered numbers increase consecutively by 1.
start1() manages the full gameplay depending on whether the user selects first (F) or second (S) chance.
In the F path, the player enters 1–3 numbers, then the computer adds 4 - inp numbers to push the sequence to a multiple of 4 and gain control.
In the S path, the computer starts first and repeatedly uses nearestMultiple() logic to force the player into saying 21.
The outer while game: loop keeps asking the user whether to play again or quit.

**Note: A winning strategy is to make the total count a multiple of 4 (4, 8, 12, 16, 20) before the opponent’s turn.

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