A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 6603240 can be evenly divided by 1 2 3 4 5 6 7 8 10 12 14 15 20 21 24 28 30 35 40 42 49 56 60 70 84 98 105 120 140 147 168 196 210 245 280 294 392 420 490 588 735 840 980 1,123 1,176 1,470 1,960 2,246 2,940 3,369 4,492 5,615 5,880 6,738 7,861 8,984 11,230 13,476 15,722 16,845 22,460 23,583 26,952 31,444 33,690 39,305 44,920 47,166 55,027 62,888 67,380 78,610 94,332 110,054 117,915 134,760 157,220 165,081 188,664 220,108 235,830 275,135 314,440 330,162 440,216 471,660 550,270 660,324 825,405 943,320 1,100,540 1,320,648 1,650,810 2,201,080 3,301,620 and 6,603,240, with no remainder.
Since 6,603,240 cannot be divided by just 1 and 6,603,240, it is not a prime number.