A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1510488 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 18 21 24 27 28 36 37 42 54 56 63 72 74 81 84 108 111 126 148 162 168 189 216 222 243 252 259 296 324 333 378 444 486 504 518 567 648 666 729 756 777 888 972 999 1,036 1,134 1,332 1,458 1,512 1,554 1,701 1,944 1,998 2,072 2,268 2,331 2,664 2,916 2,997 3,108 3,402 3,996 4,536 4,662 5,103 5,832 5,994 6,216 6,804 6,993 7,992 8,991 9,324 10,206 11,988 13,608 13,986 17,982 18,648 20,412 20,979 23,976 26,973 27,972 35,964 40,824 41,958 53,946 55,944 62,937 71,928 83,916 107,892 125,874 167,832 188,811 215,784 251,748 377,622 503,496 755,244 and 1,510,488, with no remainder.
Since 1,510,488 cannot be divided by just 1 and 1,510,488, it is not a prime number.