A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1521450 can be evenly divided by 1 2 3 5 6 7 9 10 14 15 18 21 23 25 27 30 35 42 45 46 49 50 54 63 69 70 75 90 98 105 115 126 135 138 147 150 161 175 189 207 210 225 230 245 270 294 315 322 345 350 378 414 441 450 483 490 525 575 621 630 675 690 735 805 882 945 966 1,035 1,050 1,127 1,150 1,225 1,242 1,323 1,350 1,449 1,470 1,575 1,610 1,725 1,890 2,070 2,205 2,254 2,415 2,450 2,646 2,898 3,105 3,150 3,381 3,450 3,675 4,025 4,347 4,410 4,725 4,830 5,175 5,635 6,210 6,615 6,762 7,245 7,350 8,050 8,694 9,450 10,143 10,350 11,025 11,270 12,075 13,230 14,490 15,525 16,905 20,286 21,735 22,050 24,150 28,175 30,429 31,050 33,075 33,810 36,225 43,470 50,715 56,350 60,858 66,150 72,450 84,525 101,430 108,675 152,145 169,050 217,350 253,575 304,290 507,150 760,725 and 1,521,450, with no remainder.
Since 1,521,450 cannot be divided by just 1 and 1,521,450, it is not a prime number.