  The Type II-P supernova 2004dj in the nearby galaxy NGC 2403 occurred at a
position coincident with object 96 in the list of luminous stars and clusters
in this galaxy published by Sandage in 1984. The coincidence is established
definitively through astrometric registration of our ground-based archival
images of NGC 2403 with our recent images showing the SN. The archival images
show that Sandage 96 is slightly resolved from the ground. Pre-outburst blue
spectrograms obtained by Humphreys and Aaronson reveal that Sandage 96 has a
composite spectrum, dominated in the blue region by A- and B-type stars, while
infrared photometry shows that Sandage 96 also contains red supergiants. These
results demonstrate that Sandage 96 is a young compact cluster. We have studied
the stellar population of Sandage 96, using published photometric measurements
combined with a chi-square-fitting code. We derive a cluster age of 13.6 Ma, a
reddening of E(4405-5495)=0.172, and a total stellar mass of 24 000 M_Sun. For
this cluster age, the SN progenitor had a main-sequence mass of 15 M_Sun.
Post-outburst photometry of Sandage 96 may establish whether the progenitor was
a red or blue supergiant.
