A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 901600 can be evenly divided by 1 2 4 5 7 8 10 14 16 20 23 25 28 32 35 40 46 49 50 56 70 80 92 98 100 112 115 140 160 161 175 184 196 200 224 230 245 280 322 350 368 392 400 460 490 560 575 644 700 736 784 800 805 920 980 1,120 1,127 1,150 1,225 1,288 1,400 1,568 1,610 1,840 1,960 2,254 2,300 2,450 2,576 2,800 3,220 3,680 3,920 4,025 4,508 4,600 4,900 5,152 5,600 5,635 6,440 7,840 8,050 9,016 9,200 9,800 11,270 12,880 16,100 18,032 18,400 19,600 22,540 25,760 28,175 32,200 36,064 39,200 45,080 56,350 64,400 90,160 112,700 128,800 180,320 225,400 450,800 and 901,600, with no remainder.
Since 901,600 cannot be divided by just 1 and 901,600, it is not a prime number.