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%I #6 Sep 29 2023 19:04:09
%S 1,3,15,210,26565,358999410,64449908117864115,
%T 2076895351339769396027702893296360,
%U 2156747150208372213435450937462080290024600343143329179374709804540
%N First differences of successive iterated triangular numbers with seed 2.
%C Also a triangular number -- follows from the definition of A007501.
%F a(n) = T(x(n-1))-x(n-1) where x(n)=T(x(n-1)) and T(x)=x*(x+1)/2.
%e a(1)=T(2)-2.
%e a(2)=T(3)-3.
%e a(3)=T(6)-6.
%Y First differences of successive terms of sequence A007501.
%Y Cf. A000217.
%K easy,nonn
%O 1,2
%A _Greg Huber_, Oct 06 2008
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