In Arno van den Essen's book I found a trimagic 12x12 square and that is the smallest possible trimagic (= multimagic-3) square. The trimagic square is a simple magic square, but also if you fill in (instead of number) number x number or number x number x number, you get a valid (not pure) magic square; see below.
870 | 870 | 870 | 870 | 870 | 870 | 870 | 870 | 870 | 870 | 870 | 870 | |||
870 | 870 | |||||||||||||
870 | 1 | 22 | 33 | 41 | 62 | 66 | 79 | 83 | 104 | 112 | 123 | 144 | ||
870 | 9 | 119 | 45 | 115 | 107 | 93 | 52 | 38 | 30 | 100 | 26 | 136 | ||
870 | 75 | 141 | 35 | 48 | 57 | 14 | 131 | 88 | 97 | 110 | 4 | 70 | ||
870 | 74 | 8 | 106 | 49 | 12 | 43 | 102 | 133 | 96 | 39 | 137 | 71 | ||
870 | 140 | 101 | 124 | 42 | 60 | 37 | 108 | 85 | 103 | 21 | 44 | 5 | ||
870 | 122 | 76 | 142 | 86 | 67 | 126 | 19 | 78 | 59 | 3 | 69 | 23 | ||
870 | 55 | 27 | 95 | 135 | 130 | 89 | 56 | 15 | 10 | 50 | 118 | 90 | ||
870 | 132 | 117 | 68 | 91 | 11 | 99 | 46 | 134 | 54 | 77 | 28 | 13 | ||
870 | 73 | 64 | 2 | 121 | 109 | 32 | 113 | 36 | 24 | 143 | 81 | 72 | ||
870 | 58 | 98 | 84 | 116 | 138 | 16 | 129 | 7 | 29 | 61 | 47 | 87 | ||
870 | 80 | 34 | 105 | 6 | 92 | 127 | 18 | 53 | 139 | 40 | 111 | 65 | ||
870 | 51 | 63 | 31 | 20 | 25 | 128 | 17 | 120 | 125 | 114 | 82 | 94 |
83810 | 83810 | 83810 | 83810 | 83810 | 83810 | 83810 | 83810 | 83810 | 83810 | 83810 | 83810 | |||
83810 | 83810 | |||||||||||||
83810 | 1 | 484 | 1089 | 1681 | 3844 | 4356 | 6241 | 6889 | 10816 | 12544 | 15129 | 20736 | ||
83810 | 81 | 14161 | 2025 | 13225 | 11449 | 8649 | 2704 | 1444 | 900 | 10000 | 676 | 18496 | ||
83810 | 5625 | 19881 | 1225 | 2304 | 3249 | 196 | 17161 | 7744 | 9409 | 12100 | 16 | 4900 | ||
83810 | 5476 | 64 | 11236 | 2401 | 144 | 1849 | 10404 | 17689 | 9216 | 1521 | 18769 | 5041 | ||
83810 | 19600 | 10201 | 15376 | 1764 | 3600 | 1369 | 11664 | 7225 | 10609 | 441 | 1936 | 25 | ||
83810 | 14884 | 5776 | 20164 | 7396 | 4489 | 15876 | 361 | 6084 | 3481 | 9 | 4761 | 529 | ||
83810 | 3025 | 729 | 9025 | 18225 | 16900 | 7921 | 3136 | 225 | 100 | 2500 | 13924 | 8100 | ||
83810 | 17424 | 13689 | 4624 | 8281 | 121 | 9801 | 2116 | 17956 | 2916 | 5929 | 784 | 169 | ||
83810 | 5329 | 4096 | 4 | 14641 | 11881 | 1024 | 12769 | 1296 | 576 | 20449 | 6561 | 5184 | ||
83810 | 3364 | 9604 | 7056 | 13456 | 19044 | 256 | 16641 | 49 | 841 | 3721 | 2209 | 7569 | ||
83810 | 6400 | 1156 | 11025 | 36 | 8464 | 16129 | 324 | 2809 | 19321 | 1600 | 12321 | 4225 | ||
83810 | 2601 | 3969 | 961 | 400 | 625 | 16384 | 289 | 14400 | 15625 | 12996 | 6724 | 8836 |
9082800 | 9082800 | 9082800 | 9082800 | 9082800 | 9082800 | 9082800 | 9082800 | 9082800 | 9082800 | 9082800 | 9082800 | |||
9082800 | 9082800 | |||||||||||||
9082800 | 1 | 10648 | 35937 | 68921 | 238328 | 287496 | 493039 | 571787 | 1124864 | 1404928 | 1860867 | 2985984 | ||
9082800 | 729 | 1685159 | 91125 | 1520875 | 1225043 | 804357 | 140608 | 54872 | 27000 | 1000000 | 17576 | 2515456 | ||
9082800 | 421875 | 2803221 | 42875 | 110592 | 185193 | 2744 | 2248091 | 681472 | 912673 | 1331000 | 64 | 343000 | ||
9082800 | 405224 | 512 | 1191016 | 117649 | 1728 | 79507 | 1061208 | 2352637 | 884736 | 59319 | 2571353 | 357911 | ||
9082800 | 2744000 | 1030301 | 1906624 | 74088 | 216000 | 50653 | 1259712 | 614125 | 1092727 | 9261 | 85184 | 125 | ||
9082800 | 1815848 | 438976 | 2863288 | 636056 | 300763 | 2000376 | 6859 | 474552 | 205379 | 27 | 328509 | 12167 | ||
9082800 | 166375 | 19683 | 857375 | 2460375 | 2197000 | 704969 | 175616 | 3375 | 1000 | 125000 | 1643032 | 729000 | ||
9082800 | 2299968 | 1601613 | 314432 | 753571 | 1331 | 970299 | 97336 | 2406104 | 157464 | 456533 | 21952 | 2197 | ||
9082800 | 389017 | 262144 | 8 | 1771561 | 1295029 | 32768 | 1442897 | 46656 | 13824 | 2924207 | 531441 | 373248 | ||
9082800 | 195112 | 941192 | 592704 | 1560896 | 2628072 | 4096 | 2146689 | 343 | 24389 | 226981 | 103823 | 658503 | ||
9082800 | 512000 | 39304 | 1157625 | 216 | 778688 | 2048383 | 5832 | 148877 | 2685619 | 64000 | 1367631 | 274625 | ||
9082800 | 132651 | 250047 | 29791 | 8000 | 15625 | 2097152 | 4913 | 1728000 | 1953125 | 1481544 | 551368 | 830584 |
To be honoust, I did not discover the secret of this trimagic square. Maybe you can discover the secret yourself.