A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 761600 can be evenly divided by 1 2 4 5 7 8 10 14 16 17 20 25 28 32 34 35 40 50 56 64 68 70 80 85 100 112 119 128 136 140 160 170 175 200 224 238 256 272 280 320 340 350 400 425 448 476 544 560 595 640 680 700 800 850 896 952 1,088 1,120 1,190 1,280 1,360 1,400 1,600 1,700 1,792 1,904 2,176 2,240 2,380 2,720 2,800 2,975 3,200 3,400 3,808 4,352 4,480 4,760 5,440 5,600 5,950 6,400 6,800 7,616 8,960 9,520 10,880 11,200 11,900 13,600 15,232 19,040 21,760 22,400 23,800 27,200 30,464 38,080 44,800 47,600 54,400 76,160 95,200 108,800 152,320 190,400 380,800 and 761,600, with no remainder.
Since 761,600 cannot be divided by just 1 and 761,600, it is not a prime number.