Why does summation start at k=0 in this series?

[StevenJacobs990]

n
∑ 3
k=0

How does this make sense when k=0?

 

[Gene Naden]

The sum is $3+3+...=3(n+1)$

 

[StevenJacobs990]

The sum is $3+3+...=3(n+1)$

Oh okay. The lower bound is the index origin and doesn't matter if it is negative?
n
∑ 3
k=-1
3+3+...=3(n+2)

 

[Gene Naden]

Correct!

 

[DrClaude]

To summarise,
$$
\sum_{k=a}^{b} c = c (b-a+1)
$$
for constant $c$.

 

[jbriggs444]

To summarise,
$$
\sum_{k=a}^{b} c = c (b-a+1)
$$
for constant $c$.

i.e. one is counting fence posts, not sections of wire.