Use 3x3 the same 7x7 magic square and 3x3 the '7x7 blown up' 3x3 magic square to produce a (simple) 21x21 magic square.
Take a number from the first grid and add (number -/- 1) x 49 of the same cell from the second grid.
1x number
1 | 35 | 16 | 45 | 39 | 26 | 13 | 1 | 35 | 16 | 45 | 39 | 26 | 13 | 1 | 35 | 16 | 45 | 39 | 26 | 13 |
47 | 41 | 22 | 14 | 2 | 31 | 18 | 47 | 41 | 22 | 14 | 2 | 31 | 18 | 47 | 41 | 22 | 14 | 2 | 31 | 18 |
10 | 4 | 33 | 20 | 43 | 42 | 23 | 10 | 4 | 33 | 20 | 43 | 42 | 23 | 10 | 4 | 33 | 20 | 43 | 42 | 23 |
21 | 44 | 38 | 25 | 12 | 6 | 29 | 21 | 44 | 38 | 25 | 12 | 6 | 29 | 21 | 44 | 38 | 25 | 12 | 6 | 29 |
27 | 8 | 7 | 30 | 17 | 46 | 40 | 27 | 8 | 7 | 30 | 17 | 46 | 40 | 27 | 8 | 7 | 30 | 17 | 46 | 40 |
32 | 19 | 48 | 36 | 28 | 9 | 3 | 32 | 19 | 48 | 36 | 28 | 9 | 3 | 32 | 19 | 48 | 36 | 28 | 9 | 3 |
37 | 24 | 11 | 5 | 34 | 15 | 49 | 37 | 24 | 11 | 5 | 34 | 15 | 49 | 37 | 24 | 11 | 5 | 34 | 15 | 49 |
1 | 35 | 16 | 45 | 39 | 26 | 13 | 1 | 35 | 16 | 45 | 39 | 26 | 13 | 1 | 35 | 16 | 45 | 39 | 26 | 13 |
47 | 41 | 22 | 14 | 2 | 31 | 18 | 47 | 41 | 22 | 14 | 2 | 31 | 18 | 47 | 41 | 22 | 14 | 2 | 31 | 18 |
10 | 4 | 33 | 20 | 43 | 42 | 23 | 10 | 4 | 33 | 20 | 43 | 42 | 23 | 10 | 4 | 33 | 20 | 43 | 42 | 23 |
21 | 44 | 38 | 25 | 12 | 6 | 29 | 21 | 44 | 38 | 25 | 12 | 6 | 29 | 21 | 44 | 38 | 25 | 12 | 6 | 29 |
27 | 8 | 7 | 30 | 17 | 46 | 40 | 27 | 8 | 7 | 30 | 17 | 46 | 40 | 27 | 8 | 7 | 30 | 17 | 46 | 40 |
32 | 19 | 48 | 36 | 28 | 9 | 3 | 32 | 19 | 48 | 36 | 28 | 9 | 3 | 32 | 19 | 48 | 36 | 28 | 9 | 3 |
37 | 24 | 11 | 5 | 34 | 15 | 49 | 37 | 24 | 11 | 5 | 34 | 15 | 49 | 37 | 24 | 11 | 5 | 34 | 15 | 49 |
1 | 35 | 16 | 45 | 39 | 26 | 13 | 1 | 35 | 16 | 45 | 39 | 26 | 13 | 1 | 35 | 16 | 45 | 39 | 26 | 13 |
47 | 41 | 22 | 14 | 2 | 31 | 18 | 47 | 41 | 22 | 14 | 2 | 31 | 18 | 47 | 41 | 22 | 14 | 2 | 31 | 18 |
10 | 4 | 33 | 20 | 43 | 42 | 23 | 10 | 4 | 33 | 20 | 43 | 42 | 23 | 10 | 4 | 33 | 20 | 43 | 42 | 23 |
21 | 44 | 38 | 25 | 12 | 6 | 29 | 21 | 44 | 38 | 25 | 12 | 6 | 29 | 21 | 44 | 38 | 25 | 12 | 6 | 29 |
27 | 8 | 7 | 30 | 17 | 46 | 40 | 27 | 8 | 7 | 30 | 17 | 46 | 40 | 27 | 8 | 7 | 30 | 17 | 46 | 40 |
32 | 19 | 48 | 36 | 28 | 9 | 3 | 32 | 19 | 48 | 36 | 28 | 9 | 3 | 32 | 19 | 48 | 36 | 28 | 9 | 3 |
37 | 24 | 11 | 5 | 34 | 15 | 49 | 37 | 24 | 11 | 5 | 34 | 15 | 49 | 37 | 24 | 11 | 5 | 34 | 15 | 49 |
+ 49x (number -/- 1)
2 | 2 | 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
2 | 2 | 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
2 | 2 | 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
2 | 2 | 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
2 | 2 | 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
2 | 2 | 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
2 | 2 | 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
7 | 7 | 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
7 | 7 | 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
7 | 7 | 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
7 | 7 | 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
7 | 7 | 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
7 | 7 | 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
7 | 7 | 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 8 | 8 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 8 | 8 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 8 | 8 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 8 | 8 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 8 | 8 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 8 | 8 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 8 | 8 |
= (simple) 21x21 magic square
50 | 84 | 65 | 94 | 88 | 75 | 62 | 393 | 427 | 408 | 437 | 431 | 418 | 405 | 148 | 182 | 163 | 192 | 186 | 173 | 160 |
96 | 90 | 71 | 63 | 51 | 80 | 67 | 439 | 433 | 414 | 406 | 394 | 423 | 410 | 194 | 188 | 169 | 161 | 149 | 178 | 165 |
59 | 53 | 82 | 69 | 92 | 91 | 72 | 402 | 396 | 425 | 412 | 435 | 434 | 415 | 157 | 151 | 180 | 167 | 190 | 189 | 170 |
70 | 93 | 87 | 74 | 61 | 55 | 78 | 413 | 436 | 430 | 417 | 404 | 398 | 421 | 168 | 191 | 185 | 172 | 159 | 153 | 176 |
76 | 57 | 56 | 79 | 66 | 95 | 89 | 419 | 400 | 399 | 422 | 409 | 438 | 432 | 174 | 155 | 154 | 177 | 164 | 193 | 187 |
81 | 68 | 97 | 85 | 77 | 58 | 52 | 424 | 411 | 440 | 428 | 420 | 401 | 395 | 179 | 166 | 195 | 183 | 175 | 156 | 150 |
86 | 73 | 60 | 54 | 83 | 64 | 98 | 429 | 416 | 403 | 397 | 426 | 407 | 441 | 184 | 171 | 158 | 152 | 181 | 162 | 196 |
295 | 329 | 310 | 339 | 333 | 320 | 307 | 197 | 231 | 212 | 241 | 235 | 222 | 209 | 99 | 133 | 114 | 143 | 137 | 124 | 111 |
341 | 335 | 316 | 308 | 296 | 325 | 312 | 243 | 237 | 218 | 210 | 198 | 227 | 214 | 145 | 139 | 120 | 112 | 100 | 129 | 116 |
304 | 298 | 327 | 314 | 337 | 336 | 317 | 206 | 200 | 229 | 216 | 239 | 238 | 219 | 108 | 102 | 131 | 118 | 141 | 140 | 121 |
315 | 338 | 332 | 319 | 306 | 300 | 323 | 217 | 240 | 234 | 221 | 208 | 202 | 225 | 119 | 142 | 136 | 123 | 110 | 104 | 127 |
321 | 302 | 301 | 324 | 311 | 340 | 334 | 223 | 204 | 203 | 226 | 213 | 242 | 236 | 125 | 106 | 105 | 128 | 115 | 144 | 138 |
326 | 313 | 342 | 330 | 322 | 303 | 297 | 228 | 215 | 244 | 232 | 224 | 205 | 199 | 130 | 117 | 146 | 134 | 126 | 107 | 101 |
331 | 318 | 305 | 299 | 328 | 309 | 343 | 233 | 220 | 207 | 201 | 230 | 211 | 245 | 135 | 122 | 109 | 103 | 132 | 113 | 147 |
246 | 280 | 261 | 290 | 284 | 271 | 258 | 1 | 35 | 16 | 45 | 39 | 26 | 13 | 344 | 378 | 359 | 388 | 382 | 369 | 356 |
292 | 286 | 267 | 259 | 247 | 276 | 263 | 47 | 41 | 22 | 14 | 2 | 31 | 18 | 390 | 384 | 365 | 357 | 345 | 374 | 361 |
255 | 249 | 278 | 265 | 288 | 287 | 268 | 10 | 4 | 33 | 20 | 43 | 42 | 23 | 353 | 347 | 376 | 363 | 386 | 385 | 366 |
266 | 289 | 283 | 270 | 257 | 251 | 274 | 21 | 44 | 38 | 25 | 12 | 6 | 29 | 364 | 387 | 381 | 368 | 355 | 349 | 372 |
272 | 253 | 252 | 275 | 262 | 291 | 285 | 27 | 8 | 7 | 30 | 17 | 46 | 40 | 370 | 351 | 350 | 373 | 360 | 389 | 383 |
277 | 264 | 293 | 281 | 273 | 254 | 248 | 32 | 19 | 48 | 36 | 28 | 9 | 3 | 375 | 362 | 391 | 379 | 371 | 352 | 346 |
282 | 269 | 256 | 250 | 279 | 260 | 294 | 37 | 24 | 11 | 5 | 34 | 15 | 49 | 380 | 367 | 354 | 348 | 377 | 358 | 392 |
I have used method composite, simple to construct
9x9, 12x12, 15x15a, 15x15b, 18x18, 20x20, 21x21a, 21x21b, 24x24a, 24x24b, 25x25, 27x27a, 27x27b, 28x28, 30x30a, 30x30b