For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Education/openSUSE_Tumbleweed/Education.repo
zypper refresh
zypper install yacas
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Education/15.6/Education.repo
zypper refresh
zypper install yacas
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Education/15.5/Education.repo
zypper refresh
zypper install yacas
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Education/15.4/Education.repo
zypper refresh
zypper install yacas
For 15.3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Education/15.3/Education.repo
zypper refresh
zypper install yacas