The entry is ambiguous, it is either intended to be 42*log-base42(1701) or 42*log(1701)/42 or an exponent as in 42^(log-based42(1701)), etc. etc.

The log should be entered with the toolbar button which shows 'log' or 'ln'.  "log" is a base-10 log and "ln" is a natural exponent.  Customizing the base can be quite easily using Algebrator but for doyourmath.com simply divide a base-10 log by base-X log, as in:

42*(log(1701)/log(42))