The whole thing's like an Austin Powers movie, but here's the relevant section to the title:

Scenario I, the medium variant of the United Nations 1998 Revision, assumes an annual net intake of 760,000 migrants per year between 1995-2050, for a total of 41,800,000 net migrants during the period. Accordingly, the total population of the United States is projected to increase continuously from 267 million in 1995 to 349 million in 2050 (the results of the 1998 United Nations projections are shown in the annex tables). By 2050, out of this total population of 349 million, 59 million, or 6.8 per cent, would be post-1995 immigrants or their descendants. The population aged 15-64 would increase slowly from 174 million in 1995 to 214 million in 2050, although not in a monotonic fashion. The population aged 65 or older would rise rapidly, from 33 million in 1995 to nearly 76 million in 2050. As a result, the potential support ratio would decrease from 5.2 in 1995 to 2.8 in 2050.