In its most basic form an

magic square is
an arrangement of the numbers from

to

on a square grid in such a way
the entries on the rows, columns and two main diagonals have the same sum.
Magic squares exists for every positive
and the common sum, which
we can call magic constant is
.
For example,
and
magic squares like these
have magic constant

and

.
The first magic constants are
1, 5, 15, 34, 65, 111, 175, 260, 369, 505, 671, 870, 1105, 1379, 1695, 2056, 2465, 2925, 3439 more terms
Pictorial representation of remainders (mod 2, 3, ...,11) frequency. For a table of values and more details
click here
A graph displaying how many magic constants are multiples of the primes
p from 2 to 71. In black the ideal line 1/
p.