Search: id:A108581
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%I A108581
%S A108581 1,3,3,3,6,6,6,6,6,6,10,10,10,10,10,10,10,10,10,10,15,15,15,15,15,15,15,
%T A108581 15,15,15,15,15,15,15,15,21,21,21,21,21,21,21,21,21,21,21,21,21,21,21,
%U A108581 21,21,21,21,21,21,28,28,28,28,28,28,28,28,28,28,28,28,28,28,28,28,28
%N A108581 Positive triangular numbers repeated their own number of times.
%C A108581 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 A108581 a(1) = 1, for n>1: a(A000217(n)-1) = a(A000217(n)) = ... = a(A000217(n+1)-2) 
               = A000217(n).
%Y A108581 Cf. A000217, A002024, A072649, A074279.
%Y A108581 Sequence in context: A112669 A098529 A133774 this_sequence A073080 A057944 
               A080607
%Y A108581 Adjacent sequences: A108578 A108579 A108580 this_sequence A108582 A108583 
               A108584
%K A108581 easy,nonn
%O A108581 1,2
%A A108581 Jonathan Vos Post (jvospost3(AT)gmail.com), Jul 25 2005

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