@article{700587,
     title = {Nonstable homotopy groups of $U(n)$
               },
     booktitle = {General Topology and Its Relations to Modern Analysis and Algebra},
     series = {GDML\_Books},
     publisher = {Academia Publishing House of the Czechoslovak Academy of Sciences},
     address = {Praha},
     year = {1971},
     pages = {173-174},
     zbl = {0227.57016},
     url = {http://dml.mathdoc.fr/item/700587}
}

Krishnarao, G. V. Nonstable homotopy groups of $U(n)$
               , dans General Topology and Its Relations to Modern Analysis and Algebra, GDML_Books,  (1971), pp. 173-174. http://gdmltest.u-ga.fr/item/700587/