R is very particular about what can be contained in a vector. All the elements need to be of the same type, an moreover must be either types of number^{[1]}, logical values, or strings of text^{[2]}.
If you want a collection of elements which are of different types, or not of one of the allowed vector types, you need to use a list.
Input:

l1 < list(a=1, b=1:3)

l2 < c(sqrt, log) #
Result:
NotesEdit
 ↑ There are actually 3 types of allowed numbers: "normal" numbers, complex numbers, and simple integers. This book deals almost exclusively with the first of these.
 ↑ This is not quite true, but unless you are a computer specialist, you are unlikely to use the final type: a vectors of elements storing "raw" computer bits, see
?raw