A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1770624 can be evenly divided by 1 2 3 4 6 8 9 12 16 18 24 29 32 36 48 53 58 64 72 87 96 106 116 128 144 159 174 192 212 232 261 288 318 348 384 424 464 477 522 576 636 696 848 928 954 1,044 1,152 1,272 1,392 1,537 1,696 1,856 1,908 2,088 2,544 2,784 3,074 3,392 3,712 3,816 4,176 4,611 5,088 5,568 6,148 6,784 7,632 8,352 9,222 10,176 11,136 12,296 13,833 15,264 16,704 18,444 20,352 24,592 27,666 30,528 33,408 36,888 49,184 55,332 61,056 73,776 98,368 110,664 147,552 196,736 221,328 295,104 442,656 590,208 885,312 and 1,770,624, with no remainder.
Since 1,770,624 cannot be divided by just 1 and 1,770,624, it is not a prime number.