A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2921076 can be evenly divided by 1 2 3 4 6 9 12 17 18 27 34 36 37 43 51 54 68 74 86 102 108 111 129 148 153 172 204 222 258 306 333 387 444 459 516 612 629 666 731 774 918 999 1,161 1,258 1,332 1,462 1,548 1,591 1,836 1,887 1,998 2,193 2,322 2,516 2,924 3,182 3,774 3,996 4,386 4,644 4,773 5,661 6,364 6,579 7,548 8,772 9,546 11,322 13,158 14,319 16,983 19,092 19,737 22,644 26,316 27,047 28,638 33,966 39,474 42,957 54,094 57,276 67,932 78,948 81,141 85,914 108,188 162,282 171,828 243,423 324,564 486,846 730,269 973,692 1,460,538 and 2,921,076, with no remainder.
Since 2,921,076 cannot be divided by just 1 and 2,921,076, it is not a prime number.