A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 5151510 can be evenly divided by 1 2 3 5 6 7 9 10 13 14 15 17 18 21 26 30 34 35 37 39 42 45 51 63 65 70 74 78 85 90 91 102 105 111 117 119 126 130 153 170 182 185 195 210 221 222 234 238 255 259 273 306 315 333 357 370 390 442 455 481 510 518 546 555 585 595 629 630 663 666 714 765 777 819 910 962 1,071 1,105 1,110 1,170 1,190 1,258 1,295 1,326 1,365 1,443 1,530 1,547 1,554 1,638 1,665 1,785 1,887 1,989 2,142 2,210 2,331 2,405 2,590 2,730 2,886 3,094 3,145 3,315 3,330 3,367 3,570 3,774 3,885 3,978 4,095 4,329 4,403 4,641 4,662 4,810 5,355 5,661 6,290 6,630 6,734 7,215 7,735 7,770 8,177 8,190 8,658 8,806 9,282 9,435 9,945 10,101 10,710 11,322 11,655 13,209 13,923 14,430 15,470 16,354 16,835 18,870 19,890 20,202 21,645 22,015 23,205 23,310 24,531 26,418 27,846 28,305 30,303 33,670 39,627 40,885 43,290 44,030 46,410 49,062 50,505 56,610 57,239 60,606 66,045 69,615 73,593 79,254 81,770 101,010 114,478 122,655 132,090 139,230 147,186 151,515 171,717 198,135 245,310 286,195 303,030 343,434 367,965 396,270 515,151 572,390 735,930 858,585 1,030,302 1,717,170 2,575,755 and 5,151,510, with no remainder.
Since 5,151,510 cannot be divided by just 1 and 5,151,510, it is not a prime number.