My solution is ( <"2 is for presentation reasons)
<"2 ({~[:< [:}.L:0 [:<@i."0 $) i.3+i.4
+-------------------+-------------------+-------------------+
|157 158 159 160 161|187 188 189 190 191|217 218 219 220 221|
|163 164 165 166 167|193 194 195 196 197|223 224 225 226 227|
|169 170 171 172 173|199 200 201 202 203|229 230 231 232 233|
|175 176 177 178 179|205 206 207 208 209|235 236 237 238 239|
+-------------------+-------------------+-------------------+
|277 278 279 280 281|307 308 309 310 311|337 338 339 340 341|
|283 284 285 286 287|313 314 315 316 317|343 344 345 346 347|
|289 290 291 292 293|319 320 321 322 323|349 350 351 352 353|
|295 296 297 298 299|325 326 327 328 329|355 356 357 358 359|
+-------------------+-------------------+-------------------+
Any elegant alternatives?
R.E. Boss
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