Ok. let's break this excellent PMA image down.
(7,8,15) {7:8:82:29:53:127}
nn = 64
nn div 8 = 8
nn mod 8 = 0
(2d-1)(n-1) = (164-1)(7) = 1141
1141 div 8 = 142
1141 mod 8 = 5
(n-1) = 7
(n-1) div 8 = 0
(n-1) mod 8 = 7
(f-1) = 2d-e = 82*2-7 = 157
157 div 8 = 19
157 mod 8 = 5
mods total: 0 + 5 + 7 + 5 = 17
(17-1) / 8 = 2
so each 1Tu gets 2 units of mods, middle square gets 1 unit
Each 1Tu gets 8 units of nn
Each 1Tu gets 142 units of (2d-1)(n-1)
Each 1Tu gets 0 units of (n-1)
Each 1Tu gets 19 units of (f-1)
So for each 1Tu, the sum is:
8 + 142 + 0 + 19 = 169 for the div 8's, PLUS 2 units from the mods ( 17-1 div 8 ) = 171
171 * 8 + 1 (for the middle unit) = 1369
SQRT(1369) = 37
x+n = 37
Yeah, that works!