These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 0.98 s (backtrack: 0/20).

[ebuild  N     ] sci-mathematics/primesieve-12.3:0/12::gentoo  USE="executable -doc -test" 138 KiB
[ebuild  N     ] sci-mathematics/primecount-8.0:0/8::gentoo  USE="executable openmp -test" 1179 KiB

Total: 2 packages (2 new), Size of downloads: 1317 KiB