Within sagemath, you can access Guess as fricas.guess([1,2,5,14,42]) (after doing "sage -i fricas" on the command line, to install FriCAS). Within FriCAS, you have more options, in particular you can try to express consecutive ratios or differences as functions of the form (a + b n)^n r(n), where r is a rational function.
Christian Krattenthaler