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%I #13 Sep 03 2012 07:13:12
%S 1,2,1,3,1,2,4,2,3,1,5,4,3,6,2,1,4,5,7,2,3,1
%N Triangle read by rows in which row n lists the number of pairs of states of the subshells of the n-th shell of the nuclear shell model ordered by energy level in increasing order.
%C First differs from A212121 at a(14). The illustration of initial terms is essentially the same as the illustration of initial terms of A213372, the main entry for this sequence.
%H MIT OpenCourseWare, <a href="http://www.flickr.com/photos/mitopencourseware/3772864128/in/set-72157621892931990">Energy Levels of Nucleons in a Smoothly-Varying Potential Well</a>
%F a(n) = A213372(n)/2.
%e Written as an irregular triangle in which row n represents the n-th shell of nucleus. Note that row 4 has only one term. Triangle begins:
%e 1;
%e 2, 1;
%e 3, 1, 2;
%e 4;
%e 2, 3, 1, 5;
%e 4, 3, 6, 2, 1;
%e 4, 5, 7, 2, 3, 1;
%Y Partial sums give A213373. Other version are A004736, A130517, A212121, A213361.
%Y Cf. A213372, A213374.
%K nonn,tabf,hard,more
%O 1,2
%A _Omar E. Pol_, Jul 16 2012
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