The "magic numbers" for atoms are

$($a$)$ numbers of electrons that confer atomic stability.

$($b$)$ numbers of protons and$/$or neutrons that confer nuclear stability.

$($c$)\backslash (\backslash$mathrm$\{$n$\}/\backslash$mathrm$\{$p$\}\backslash )$ ratios that confer nuclear stability.

$($d$)$ atomic masses that confer nuclear stability.

$($e$)$ atomic masses that indicate fissile isotopes.