The number 6,666,660 can be evenly divided by 1 2 3 4 5 6 7 9 10 11 12 13 14 15 18 20 21 22 26 28 30 33 35 36 37 39 42 44 45 52 55 60 63 65 66 70 74 77 78 84 90 91 99 105 110 111 117 126 130 132 140 143 148 154 156 165 180 182 185 195 198 210 220 222 231 234 252 259 260 273 286 308 315 330 333 364 370 385 390 396 407 420 429 444 455 462 468 481 495 518 546 555 572 585 630 660 666 693 715 740 770 777 780 814 819 858 910 924 962 990 1,001 1,036 1,092 1,110 1,155 1,170 1,221 1,260 1,287 1,295 1,332 1,365 1,386 1,430 1,443 1,540 1,554 1,628 1,638 1,665 1,716 1,820 1,924 1,980 2,002 2,035 2,145 2,220 2,310 2,331 2,340 2,405 2,442 2,574 2,590 2,730 2,772 2,849 2,860 2,886 3,003 3,108 3,276 3,330 3,367 3,465 3,663 3,885 4,004 4,070 4,095 4,290 4,329 4,620 4,662 4,810 4,884 5,005 5,148 5,180 5,291 5,460 5,698 5,772 6,006 6,105 6,435 6,660 6,734 6,930 7,215 7,326 7,770 8,140 8,190 8,547 8,580 8,658 9,009 9,324 9,620 10,010 10,101 10,582 11,396 11,655 12,012 12,210 12,870 13,468 13,860 14,245 14,430 14,652 15,015 15,540 15,873 16,380 16,835 17,094 17,316 18,018 18,315 20,020 20,202 21,164 21,645 23,310 24,420 25,641 25,740 26,455 28,490 28,860 30,030 30,303 31,746 33,670 34,188 36,036 36,630 37,037 40,404 42,735 43,290 45,045 46,620 47,619 50,505 51,282 52,910 56,980 60,060 60,606 63,492 67,340 73,260 74,074 79,365 85,470 86,580 90,090 95,238 101,010 102,564 105,820 111,111 121,212 128,205 148,148 151,515 158,730 170,940 180,180 185,185 190,476 202,020 222,222 238,095 256,410 303,030 317,460 333,333 370,370 444,444 476,190 512,820 555,555 606,060 666,666 740,740 952,380 1,111,110 1,333,332 1,666,665 2,222,220 3,333,330 and 6,666,660, with no remainder.
Since 6,666,660 cannot be divided by just 1 and 6,666,660, it is a composite number.