A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3655600 can be evenly divided by 1 2 4 5 8 10 13 16 19 20 25 26 37 38 40 50 52 65 74 76 80 95 100 104 130 148 152 185 190 200 208 247 260 296 304 325 370 380 400 475 481 494 520 592 650 703 740 760 925 950 962 988 1,040 1,235 1,300 1,406 1,480 1,520 1,850 1,900 1,924 1,976 2,405 2,470 2,600 2,812 2,960 3,515 3,700 3,800 3,848 3,952 4,810 4,940 5,200 5,624 6,175 7,030 7,400 7,600 7,696 9,139 9,620 9,880 11,248 12,025 12,350 14,060 14,800 17,575 18,278 19,240 19,760 24,050 24,700 28,120 35,150 36,556 38,480 45,695 48,100 49,400 56,240 70,300 73,112 91,390 96,200 98,800 140,600 146,224 182,780 192,400 228,475 281,200 365,560 456,950 731,120 913,900 1,827,800 and 3,655,600, with no remainder.
Since 3,655,600 cannot be divided by just 1 and 3,655,600, it is not a prime number.