It looks like seq for integers bigger than 2^64 sometimes generate wrong results. There are few examples of wrong output I have found:
$ seq 18446744073709551617 inf | head -3
18446744073709551616
18446744073709551617
18446744073709551618
$
seq 10000000000000000000000000000 inf | head -3
9999999999999999999731564544
9999999999999999999731564545
9999999999999999999731564546
$
seq -1000000000000000000000000 0 | head -3
-1000000000000000000000000
-1000000000000000000000000
-1000000000000000000000000
It is similar to bug #75994 which reports the same issue but only for "-w" option.