Projective representations of finite groups over number rings

We solve the problem of finding the number $n(R,G)$ of nondecomposable projective representations of a finite group $G$ over the ring $R$ of all integers of a finite extension $F$ of the field of rational $p$-adic numbers $Q$. Also we clear up the question as to when all indecomposable projective $R$-representations of a group $G$ are realized by left ideals of crossed group rings of the group $G$ and the ring $R$. We note that for ordinary $R$-representations of a group $G$ the problem of the finiteness of the number $n(R,G)$ was investigated by S. D. Berman, I. Reiner, A. Heller, H. Yacobinski and one of the authors of the present article.
Bibliography: 30 titles.