A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1565564 can be evenly divided by 1 2 4 7 11 13 14 17 22 23 26 28 34 44 46 52 68 77 91 92 119 143 154 161 182 187 221 238 253 286 299 308 322 364 374 391 442 476 506 572 598 644 748 782 884 1,001 1,012 1,196 1,309 1,547 1,564 1,771 2,002 2,093 2,431 2,618 2,737 3,094 3,289 3,542 4,004 4,186 4,301 4,862 5,083 5,236 5,474 6,188 6,578 7,084 8,372 8,602 9,724 10,166 10,948 13,156 17,017 17,204 20,332 23,023 30,107 34,034 35,581 46,046 55,913 60,214 68,068 71,162 92,092 111,826 120,428 142,324 223,652 391,391 782,782 and 1,565,564, with no remainder.
Since 1,565,564 cannot be divided by just 1 and 1,565,564, it is not a prime number.