A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1375220 can be evenly divided by 1 2 4 5 7 10 11 14 19 20 22 28 35 38 44 47 55 70 76 77 94 95 110 133 140 154 188 190 209 220 235 266 308 329 380 385 418 470 517 532 658 665 770 836 893 940 1,034 1,045 1,316 1,330 1,463 1,540 1,645 1,786 2,068 2,090 2,585 2,660 2,926 3,290 3,572 3,619 4,180 4,465 5,170 5,852 6,251 6,580 7,238 7,315 8,930 9,823 10,340 12,502 14,476 14,630 17,860 18,095 19,646 25,004 29,260 31,255 36,190 39,292 49,115 62,510 68,761 72,380 98,230 125,020 137,522 196,460 275,044 343,805 687,610 and 1,375,220, with no remainder.
Since 1,375,220 cannot be divided by just 1 and 1,375,220, it is not a prime number.