Need help i just don't understand why this codes output is 1 3 6 10 15 21 can anyone explain

Question

def tri_recursion(k):
if(k > 0):
result = k + tri_recursion(k - 1)
print(result)
else:
result = 0
return result

print("\n\nRecursion Example Results")
tri_recursion(6)

Answer 1

For Example: k = 4
tri_recursion(4) =>
4 + tri_recursion(3)

New call
tri_recursion(3) =>
3 + tri_recursion(2)

New call
tri_recursion(2) =>
2 + tri_recursion(1)

New call
tri_recursion(1) =>
1 + tri_recursion(0) => 1 + 0
this prints 1 , and returns 1 to privoius incomplete call.

So then it's previous call is :
tri_recursion(2) =>
2 + tri_recursion(1)
= 2 + 1 => 3
print(3)
return 3 to it's previous call

tri_recursion(3) =>
3 + tri_recursion(2) => 3 + 3
this prints 6 , and returns 6 to it's previous and first call.

tri_recursion(4) =>
4 + tri_recursion(3) => 4 + 6 = 10.
You have print statement after this calculation. So it print result. And also same value is returned to function call.

Similar
(5) => 5+4+3+2+1 = 15 printing each value.
For 6: 15+6=21
For 7: 21+7=28

Hope it helps..