A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 760760 can be evenly divided by 1 2 4 5 7 8 10 11 13 14 19 20 22 26 28 35 38 40 44 52 55 56 65 70 76 77 88 91 95 104 110 130 133 140 143 152 154 182 190 209 220 247 260 266 280 286 308 364 380 385 418 440 455 494 520 532 572 616 665 715 728 760 770 836 910 988 1,001 1,045 1,064 1,144 1,235 1,330 1,430 1,463 1,540 1,672 1,729 1,820 1,976 2,002 2,090 2,470 2,660 2,717 2,860 2,926 3,080 3,458 3,640 4,004 4,180 4,940 5,005 5,320 5,434 5,720 5,852 6,916 7,315 8,008 8,360 8,645 9,880 10,010 10,868 11,704 13,585 13,832 14,630 17,290 19,019 20,020 21,736 27,170 29,260 34,580 38,038 40,040 54,340 58,520 69,160 76,076 95,095 108,680 152,152 190,190 380,380 and 760,760, with no remainder.
Since 760,760 cannot be divided by just 1 and 760,760, it is not a prime number.