for N=5, what are possible matrices (in short which one i have missed..) in abcd: 1114,1214,1124,1134,1314 (which is 52=10 when a=1,d=4 & a=4,d=1) and 2113,2123,2213,2413,2143,2133,2313,2223 which is(82=16 when a=2,d=3 & a=3,d=2)..total 26..bt the ans is 30...(multipilied by 2 as when "a" and "d" are interchanged they will produce the similar pattern.)
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