Let S be a finite set of integers, do I can check with Gap that this set be a set of character degrees of small group?



character degree in Gap
Dima is correct that the problem is much easier with multisets. Furthermore, taking direct products with Abelian groups, it is clear that for any given set of irreducible character degrees which actually occurs, there are infinitely many groups for which it occurs, if we allow multiplicities. I had a recollection that Isaacs and Passman proved a kind of converse of this: if a finite group $G$ has all its irreducible character degrees of degree less than $d,$ then $G$ has an Abelian normal subgroup $A$ whose index is bounded in terms of $d.$ I could not locate a reference at the time, though I did not have Isaacs' book to hand. 
Since my original post, however, Yemon Choi kindly provided a reference in the comments below (see MR0167539). The wording of Isaacs and Passman's result is perhaps mildly ambiguos: they speak of an Abelian subgroup of index bounded in terms of $d$, omitting the word "normal", but of course if $G$ has an Abelian subgroup $A$ with $[G:A] \leq h,$ then the intersection of the $G$-conjugates of $A$ is normal, and has index at most $h!$.
 Hence, in general, if we know the irreducible character degrees of a finite group $H,$ there is an Abelian normal subgroup $A$ of $H$ such that $|H/A|$ is bounded in terms of the largest degree. So in small cases, it may be possible to use GAP to determine all possibilities for $H/A.$


