Python Program for Print Number Series Without Using any Loop (original) (raw)

Last Updated : 30 Oct, 2025

Given two numbers N and K, the task is to print a number series where each term is obtained by repeatedly subtracting K from N until the number becomes zero or negative and once it becomes zero or negative, we start adding K back until the number reaches the original value N again. You must do this without using any loop.

**For Example:

**Input: N = 15, K = 5
**Output: 15 10 5 0 -5 0 5 10 15

**Input: N = 20, K = 6
**Output: 20 14 8 2 -4 2 8 14 20

Let's explore different methods to print number series without using loop in Python.

Recursive Mathematical Approach

This method uses recursion to repeatedly subtract and add the number K. The same function calls itself until number becomes zero or negative and then reverses back to the original value, forming the full pattern automatically.

Python `

def print_series(N, K): if N <= 0: print(N, end=" ") return print(N, end=" ") print_series(N - K, K) print(N, end=" ")

N = 20 K = 6 print_series(N, K)

Output

20 14 8 2 -4 2 8 14 20

**Explanation:

def print_series(N, K): defines a recursive function to print the series.
if N <= 0: stops subtracting once N becomes zero or negative.
print(N, end=" ") prints the current number without going to a new line.
print_series(N - K, K) recursively calls itself with the reduced number.

Recursive Toggle Approach Using a Boolean Flag

This method introduces a flag variable to control whether the program should subtract or add K. Once the number becomes zero or negative, the flag flips, and the recursion direction reverses automatically.

Python `

def print_number(N, original, K, flag): print(N, end=" ")

if N <= 0:
    flag = not flag

if N == original and not flag:
    return

if flag:
    print_number(N - K, original, K, flag)
else:
    print_number(N + K, original, K, flag)

N = 20 K = 6 print_number(N, N, K, True)

Output

20 14 8 2 -4 2 8 14 20

**Explanation:

print_number(N, original, K, flag) prints the number and decides next operation.
flag decides whether to subtract or add.
When N <= 0, flag switches from True to False, changing direction.
The recursion continues until the number returns to its original value.

Recursive One-Liner (Lambda Expression)

This method uses a lambda function (anonymous function) and Python’s recursive nature in a single line. It’s compact and demonstrates recursion elegantly.

Python `

f = lambda n, k: print(n, end=" ") or (f(n - k, k) or print(n, end=" ")) if n > 0 else print(n, end=" ") f(20, 6)

Output

20 14 8 2 -4 2 8 14 20

**Explanation:

lambda defines an inline recursive function without a name.
print(n, end=" ") prints each number in sequence.
Uses or chaining to ensure both subtraction and reprinting occur properly.

Using Recursion with List Storage and Unpacking

This method stores the entire recursive series inside a list and then prints it using the * unpacking operator for clean output.

Python `

def series(n, k): return [n] if n <= 0 else [n] + series(n - k, k) + [n]

N, K = 20, 6 print(*series(N, K))

Output

20 14 8 2 -4 2 8 14 20

**Explanation:

series(n, k) builds a list recursively by joining decreasing and increasing parts.
When n <= 0, recursion stops and returns [n].
The final list is printed using print(*list), which expands and prints all elements in one line.

Please refer complete article on Print Number series without using any loop for more details!