Entering hexadecimal numbers?



I have some long hexadecimal numbers (48 hex digits) I want to use.  But
ibase:16 doesn't seem to accept non-numeric characters as input:

(%i1) ibase:16$
(%i2) 1000;
(%o2)                              4096
(%i3) FF24;
(%o3)                              FF24,

Can anybody enlighten me here?  Oh: Maxima 5.15.0, on linux, using clisp.

Thanks,
Alasdair