A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2387385 can be evenly divided by 1 3 5 7 9 11 13 15 21 33 35 39 45 53 55 63 65 77 91 99 105 117 143 159 165 195 231 265 273 315 371 385 429 455 477 495 583 585 689 693 715 795 819 1,001 1,113 1,155 1,287 1,365 1,749 1,855 2,067 2,145 2,385 2,915 3,003 3,339 3,445 3,465 4,081 4,095 4,823 5,005 5,247 5,565 6,201 6,435 7,579 8,745 9,009 10,335 12,243 14,469 15,015 16,695 20,405 22,737 24,115 26,235 31,005 36,729 37,895 43,407 45,045 53,053 61,215 68,211 72,345 113,685 159,159 183,645 217,035 265,265 341,055 477,477 795,795 and 2,387,385, with no remainder.
Since 2,387,385 cannot be divided by just 1 and 2,387,385, it is not a prime number.