A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 794580 can be evenly divided by 1 2 3 4 5 6 10 12 15 17 19 20 30 34 38 41 51 57 60 68 76 82 85 95 102 114 123 164 170 190 204 205 228 246 255 285 323 340 380 410 492 510 570 615 646 697 779 820 969 1,020 1,140 1,230 1,292 1,394 1,558 1,615 1,938 2,091 2,337 2,460 2,788 3,116 3,230 3,485 3,876 3,895 4,182 4,674 4,845 6,460 6,970 7,790 8,364 9,348 9,690 10,455 11,685 13,243 13,940 15,580 19,380 20,910 23,370 26,486 39,729 41,820 46,740 52,972 66,215 79,458 132,430 158,916 198,645 264,860 397,290 and 794,580, with no remainder.
Since 794,580 cannot be divided by just 1 and 794,580, it is not a prime number.