The number 3,921,408 can be evenly divided by 1 2 3 4 6 8 9 12 16 18 23 24 32 36 37 46 48 64 69 72 74 92 96 111 128 138 144 148 184 192 207 222 256 276 288 296 333 368 384 414 444 512 552 576 592 666 736 768 828 851 888 1,104 1,152 1,184 1,332 1,472 1,536 1,656 1,702 1,776 2,208 2,304 2,368 2,553 2,664 2,944 3,312 3,404 3,552 4,416 4,608 4,736 5,106 5,328 5,888 6,624 6,808 7,104 7,659 8,832 9,472 10,212 10,656 11,776 13,248 13,616 14,208 15,318 17,664 18,944 20,424 21,312 26,496 27,232 28,416 30,636 35,328 40,848 42,624 52,992 54,464 56,832 61,272 81,696 85,248 105,984 108,928 122,544 163,392 170,496 217,856 245,088 326,784 435,712 490,176 653,568 980,352 1,307,136 1,960,704 and 3,921,408, with no remainder.
Since 3,921,408 cannot be divided by just 1 and 3,921,408, it is a composite number.