A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1743768 can be evenly divided by 1 2 3 4 6 8 9 12 13 18 23 24 26 27 36 39 46 52 54 69 72 78 81 92 104 108 117 138 156 162 184 207 216 234 243 276 299 312 324 351 414 468 486 552 598 621 648 702 729 828 897 936 972 1,053 1,196 1,242 1,404 1,458 1,656 1,794 1,863 1,944 2,106 2,392 2,484 2,691 2,808 2,916 3,159 3,588 3,726 4,212 4,968 5,382 5,589 5,832 6,318 7,176 7,452 8,073 8,424 9,477 10,764 11,178 12,636 14,904 16,146 16,767 18,954 21,528 22,356 24,219 25,272 32,292 33,534 37,908 44,712 48,438 64,584 67,068 72,657 75,816 96,876 134,136 145,314 193,752 217,971 290,628 435,942 581,256 871,884 and 1,743,768, with no remainder.
Since 1,743,768 cannot be divided by just 1 and 1,743,768, it is not a prime number.