Nickel-62

Nickel-62 is a stable isotope of nickel, having 28 protons and 34 neutrons.
It has the highest binding energy per nucleon of any known nuclide. It is often stated that is the "most stable nucleus", but this is because ⁵⁶Fe has the lowest mass per nucleon, not binding energy per nucleon, of all nuclides. The lower mass per nucleon of ⁵⁶Fe is possible because ⁵⁶Fe has 26/56 ≈ 46.43% protons, while ⁶²Ni has only 28/62 ≈ 45.16% protons. Protons are less massive than neutrons, meaning that the larger fraction of protons in ⁵⁶Fe lowers its mean mass per nucleon without changing its binding energy, which is by definition measured with respect to the actual mix of protons and neutrons in the nucleus In other words, nickel-62 can be said to have the 'least massive' protons and neutrons of any isotope.

Properties

The high binding energy of nickel isotopes in general makes nickel an "end product" of many nuclear reactions throughout the universe and accounts for the high relative abundance of nickel—although most nickel in space is nickel-58 and nickel-60, with the other stable isotopes being quite rare. This suggests that most nickel is produced in supernovas in the r-process of neutron capture from nickel-56 immediately after the core-collapse, with any nickel-56 that escapes the supernova explosion rapidly decaying to cobalt-56 and then stable iron-56.

Relationship to iron-56

The second and third most tightly bound nuclei are those of Fe and Fe, with binding energies per nucleon of 8.7922 MeV and 8.7903 MeV, respectively.
As noted above, the isotope Fe has the lowest mass per nucleon of any nuclide, 930.412 MeV/c, followed by Ni with 930.417 MeV/c and Ni with 930.420 MeV/c. This does not contradict the binding energy numbers because Ni has a greater proportion of neutrons which are more massive than protons.
The misconception of Fe's higher nuclear binding energy probably originated from astrophysics. During nucleosynthesis in stars the competition between photodisintegration and alpha capturing causes more Ni to be produced than Ni. The Ni is the natural end product of silicon-burning at the end of a supernova's life and is the product of 14 alpha captures in the alpha process which builds more massive elements in steps of 4 nucleons, from carbon. This alpha process in supernovas burning ends here because of the production of zinc-60, which would be the next step after addition of another "alpha", is unfavorable.
Nonetheless, 28 atoms of nickel-62 fusing into 31 atoms of iron-56 releases 5.7 keV per nucleon; hence the future of an expanding universe without proton decay includes iron stars rather than "nickel stars".