Install this version:
emerge -a =sci-mathematics/calc-2.17.0.0
If this version is masked, you can unmask it using the autounmask tool or standard emerge options:
autounmask
emerge
autounmask =sci-mathematics/calc-2.17.0.0
Or alternatively:
emerge --autounmask-write -a =sci-mathematics/calc-2.17.0.0
calc-2.16.1.3.ebuild