A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3665664 can be evenly divided by 1 2 3 4 6 8 9 12 16 18 24 32 36 37 43 48 64 72 74 86 96 111 128 129 144 148 172 192 222 256 258 288 296 333 344 384 387 444 516 576 592 666 688 768 774 888 1,032 1,152 1,184 1,332 1,376 1,548 1,591 1,776 2,064 2,304 2,368 2,664 2,752 3,096 3,182 3,552 4,128 4,736 4,773 5,328 5,504 6,192 6,364 7,104 8,256 9,472 9,546 10,656 11,008 12,384 12,728 14,208 14,319 16,512 19,092 21,312 24,768 25,456 28,416 28,638 33,024 38,184 42,624 49,536 50,912 57,276 76,368 85,248 99,072 101,824 114,552 152,736 203,648 229,104 305,472 407,296 458,208 610,944 916,416 1,221,888 1,832,832 and 3,665,664, with no remainder.
Since 3,665,664 cannot be divided by just 1 and 3,665,664, it is not a prime number.