Python Number Triangle Pattern (Starting from 11)

What Is This Pattern?

An increasing number triangle from 11 prints i values on row i, each computed as 9 + i + j — so the first cell is always 11.

Rule: for i from 1 to rows
        for j from 1 to i
          print (9 + i + j) and a space

11
12 13
13 14 15
14 15 16 17
15 16 17 18 19     ← rows = 5

Follows the number-star diamond in Program 31; next is the same shape starting from 1 in Program 33.

How to Solve It

Outer loop grows i. Inner loop prints i values with the formula 9 + i + j, separated by spaces.

Pseudocode

for i from 1 to rows:
    for j from 1 to i:
        print (9 + i + j) and a space
    print newline

Cheat sheet

Printing Numbers vs Starting a New Line

Print each value with a trailing space, then break once with print(). Putting print() inside the inner loop prints one number per line.

Live Preview

Change the row count and the increasing triangle updates instantly.

11 
12 13 
13 14 15 
14 15 16 17 
15 16 17 18 19 

Worked Walkthrough — rows = 5

Trace how each (i, j) pair maps to 9 + i + j.

Total numbers = 1 + 2 + … + n = n(n+1)/2 → O(n²).

Python Programs

Three complete programs: fixed rows = 5, custom base with input(), and compact rows = 3. Use View Output for sample results.

for i in range(1, 6):
    for j in range(1, i + 1):
        print(9 + i + j, end=" ")
    print()

11 
12 13 
13 14 15 
14 15 16 17 
15 16 17 18 19 

rows = int(input("Enter rows: "))
base_val = int(input("Enter base: "))

if rows < 1:
    print("Please enter a positive integer for rows.")
else:
    for i in range(1, rows + 1):
        for j in range(1, i + 1):
            print(base_val + i + j, end=" ")
        print()

Enter rows: 3
Enter base: 9
11 
12 13 
13 14 15 

raw = input("Enter rows: ").strip()
try:
    rows = int(raw)
except ValueError:
    print("Please enter a positive integer.")
    raise SystemExit(1)
if rows < 1:
    print("Please enter a positive integer.")
    raise SystemExit(1)

rows = 3

for i in range(1, rows + 1):
    for j in range(1, i + 1):
        print(9 + i + j, end=" ")
    print()

11 
12 13 
13 14 15 

Time and Space Complexity

Row i prints i numbers. Total = 1 + 2 + … + n = n(n+1)/2 → O(n²) time. Only a few loop variables are needed.

Key Takeaways