why not review a bit Your understanding of the representation of numbers in the different bases,
and the relative limit for the maximum number of digits that can be represented
a stupid programmers hand calculator would have shown that
18446744073709551615 is the greatest unsigned that can be represented in 64 bits
as a reminder here is the powers of 2 table up to 2**64
2**00 1
2**01 2
2**02 4
2**03 8
2**04 16
2**05 32
2**06 64
2**07 128
2**08 256
2**09 512
2**10 1024
2**11 2048
2**12 4096
2**13 8192
2**14 16384
2**15 32768
2**16 65536
2**17 131072
2**18 262144
2**19 524288
2**20 1048576
2**21 2097152
2**22 4194304
2**23 8388608
2**24 16777216
2**25 33554432
2**26 67108864
2**27 134217728
2**28 268435456
2**29 536870912
2**30 1073741824
2**31 2147483648
2**32 4294967296
2**33 8589934592
2**34 17179869184
2**35 34359738368
2**36 68719476736
2**37 137438953472
2**38 274877906944
2**39 549755813888
2**40 1099511627776
2**41 2199023255552
2**42 4398046511104
2**43 8796093022208
2**44 17592186044416
2**45 35184372088832
2**46 70368744177664
2**47 140737488355328
2**48 281474976710656
2**49 562949953421312
2**50 1125899906842624
2**51 2251799813685248
2**52 4503599627370496
2**53 9007199254740992
2**54 18014398509481984
2**55 36028797018963968
2**56 72057594037927936
2**57 144115188075855872
2**58 288230376151711744
2**59 576460752303423488
2**60 1152921504606846976
2**61 2305843009213693952
2**62 4611686018427387904
2**63 9223372036854775808
2**64 18446744073709551616