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11 is equal to 2 protons. 1111 is equal 2+2 protons. 111111 is equal 2+2+2 protons...
Repunit numbers represent the subshells.
Table of n, a(n) for n=1..28.
See the model in the entry: A130517, A130556.
Cf. A056951, A130517, A130556.
Sequence in context: A191111 A127851 A135656 * A248753 A248754 A099814
Adjacent sequences: A130599 A130600 A130601 * A130603 A130604 A130605
Omar E. Pol, Aug 10 2007, Aug 12 2007