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%I #4 Mar 30 2012 18:40:28
%S 1,3,3,3,6,6,6,6,6,6,10,10,10,10,10,10,10,10,10,10,15,15,15,15,15,15,
%T 15,15,15,15,15,15,15,15,15,21,21,21,21,21,21,21,21,21,21,21,21,21,21,
%U 21,21,21,21,21,21,21,28,28,28,28,28,28,28,28,28,28,28,28,28,28,28,28,28
%N Positive triangular numbers repeated their own number of times.
%C In terms of the repetition convolution operator #, where (sequence A) # (sequence B) = the sequence consisting of A(n) copies of B(n), then this sequence is the repetition self-convolution (A000217(n)-0) # (A000217(n)-0). Over the set of positive infinite integer sequences, # gives a nonassociative noncommutative groupoid with a left identity (A000012) but no right identity, where the left identity is also a right nullifier and idempotent.
%F a(1) = 1, for n>1: a(A000217(n)-1) = a(A000217(n)) = ... = a(A000217(n+1)-2) = A000217(n).
%Y Cf. A000217, A002024, A072649, A074279.
%K easy,nonn
%O 1,2
%A _Jonathan Vos Post_, Jul 25 2005
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