For n=2, test squares with 1 layer of numbers around the center number until a square is enclosed with only nonprimes.
.
65 64 63 62 61 60 59 58 57
.
66 37 36 35 34 33 32 31 56
.
67 38 17 16 15 14 13 30 55
.
68 39 18 5 4 3 12 29 54
.
69 40 19 6 1 2 11 28 53
. ++
70 41 20 7 8 9  10 27 52 
.  
71 42 21 22 23 24  25 26 51 
.  
72 43 44 45 46 47  48 49 50 
. ++
73 74 75 76 77 78 79 80 81
.
The first number tested, 1, does not work because 2, 3, 5 and 7 are in the 1layered square and are prime. The first square that works is 26 because 10, 27, 52, 25, 26, 51, 48, 49, and 50 are all nonprime.
