1 + 8^1 = 9 OK
1 + 63 = 8^2 OK
1 + 8^3 = 513 OK
1 + 4095 = 8^4 OK
1 + 8^5 = 32769 OK
1 + 8^6 = 261243 OK
1 + 8^7 = 2097153 OK
1 + 16777215 = 8^8 OK
1 + 8^9 = 134217729 OK
1 + 1073741823 = 8^10 OK
1 + 8^11 = 8589934593 OK
1 + 68719476735 = 8^12 OK
1 + 8^13 = 549755813889 OK
綺麗です!