Remarkably 521 - 156
= 13 * 28 + 1 and 521 + 156 = 13 * 52 + 1.
28 = 4 * 7 and 52 = 4 * 13. To add 156 to 365 results in 521 = 260 + 261 = 13 * 40 + 1. To add another 156 to 365 results in 13 * 52 + 1, because 13 * 12 = 156:
The table can be extended. 209 = 13 * 16 + 1 is an obvious addition. |