A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 5131500 can be evenly divided by 1 2 3 4 5 6 10 11 12 15 20 22 25 30 33 44 50 55 60 66 75 100 110 125 132 150 165 220 250 275 300 311 330 375 500 550 622 660 750 825 933 1,100 1,244 1,375 1,500 1,555 1,650 1,866 2,750 3,110 3,300 3,421 3,732 4,125 4,665 5,500 6,220 6,842 7,775 8,250 9,330 10,263 13,684 15,550 16,500 17,105 18,660 20,526 23,325 31,100 34,210 38,875 41,052 46,650 51,315 68,420 77,750 85,525 93,300 102,630 116,625 155,500 171,050 205,260 233,250 256,575 342,100 427,625 466,500 513,150 855,250 1,026,300 1,282,875 1,710,500 2,565,750 and 5,131,500, with no remainder.
Since 5,131,500 cannot be divided by just 1 and 5,131,500, it is not a prime number.