A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3777774 can be evenly divided by 1 2 3 6 7 11 13 14 17 21 22 26 33 34 37 39 42 51 66 74 77 78 91 102 111 119 143 154 182 187 221 222 231 238 259 273 286 357 374 407 429 442 462 481 518 546 561 629 663 714 777 814 858 962 1,001 1,122 1,221 1,258 1,309 1,326 1,443 1,547 1,554 1,887 2,002 2,431 2,442 2,618 2,849 2,886 3,003 3,094 3,367 3,774 3,927 4,403 4,641 4,862 5,291 5,698 6,006 6,734 6,919 7,293 7,854 8,177 8,547 8,806 9,282 10,101 10,582 13,209 13,838 14,586 15,873 16,354 17,017 17,094 20,202 20,757 24,531 26,418 31,746 34,034 37,037 41,514 48,433 49,062 51,051 57,239 74,074 89,947 96,866 102,102 111,111 114,478 145,299 171,717 179,894 222,222 269,841 290,598 343,434 539,682 629,629 1,259,258 1,888,887 and 3,777,774, with no remainder.
Since 3,777,774 cannot be divided by just 1 and 3,777,774, it is not a prime number.