A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 792540 can be evenly divided by 1 2 3 4 5 6 7 9 10 12 14 15 17 18 20 21 28 30 34 35 36 37 42 45 51 60 63 68 70 74 84 85 90 102 105 111 119 126 140 148 153 170 180 185 204 210 222 238 252 255 259 306 315 333 340 357 370 420 444 476 510 518 555 595 612 629 630 666 714 740 765 777 1,020 1,036 1,071 1,110 1,190 1,258 1,260 1,295 1,332 1,428 1,530 1,554 1,665 1,785 1,887 2,142 2,220 2,331 2,380 2,516 2,590 3,060 3,108 3,145 3,330 3,570 3,774 3,885 4,284 4,403 4,662 5,180 5,355 5,661 6,290 6,660 7,140 7,548 7,770 8,806 9,324 9,435 10,710 11,322 11,655 12,580 13,209 15,540 17,612 18,870 21,420 22,015 22,644 23,310 26,418 28,305 37,740 39,627 44,030 46,620 52,836 56,610 66,045 79,254 88,060 113,220 132,090 158,508 198,135 264,180 396,270 and 792,540, with no remainder.
Since 792,540 cannot be divided by just 1 and 792,540, it is not a prime number.