Magic Constant of Magic Square
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Theorem
The magic constant of a magic square of order $n$ is given by:
- $S_n = \dfrac {n \paren {n^2 + 1} } 2$
Proof
Let $M_n$ denote a magic square of order $n$.
By Sum of Terms of Magic Square, the total of all the entries in a magic square of order $n$ is given by:
- $T_n = \dfrac {n^2 \paren {n^2 + 1} } 2$
There are $n$ rows in $M_n$, each one with the same magic constant.
Thus the magic constant $S_n$ of the magic square $M_n$ is given by:
\(\ds S_n\) | \(=\) | \(\ds \dfrac {T_n} n\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds \dfrac {n^2 \paren {n^2 + 1} } {2 n}\) | Sum of Terms of Magic Square | |||||||||||
\(\ds \) | \(=\) | \(\ds \dfrac {n \paren {n^2 + 1} } 2\) |
$\blacksquare$
Sequence
The sequence of the magic constants of magic squares of order $n$ begins:
- $1, (5,) \, 15, 34, 65, 111, 175, 260, 369, 505, 671, 870, 1105, 1379, 1695, 2056, 2465, 2925, 3439, \ldots$
However, note that while $5 = \dfrac {2 \paren {2^2 + 1} } 2$, a magic square of order $2$ does not actually exist.