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%I #18 Mar 12 2021 22:24:42
%S 0,0,0,1,0,1,0,1,2,0,1,2,0,1,2,3,0,1,2,3,0,1,2,3,4,0,1,2,3,4,0,1,2,3,
%T 4,5,0,1,2,3,4,5,0,1,2,3,4,5,6,0,1,2,3,4,5,6,0,1,2,3,4,5,6,7,0,1,2,3,
%U 4,5,6,7,0,1,2,3,4,5,6,7,8,0,1,2,3,4,5,6,7,8,0,1,2,3,4,5,6,7,8,9,0,1
%N Integers 0..n then 0..n then 0..n+1 then 0..n+1 etc.
%C Second column in the monotonic justified array of all positive generalized Fibonacci sequences (A160271). see also A199474. - Casey Mongoven, Nov 06 2011
%C Can also be seen as an irregular triangle with duplicated rows of A002262. - _Reinhard Zumkeller_, Jul 14 2015
%H Reinhard Zumkeller, <a href="/A055087/b055087.txt">Rows n = 0..120 of triangle, flattened</a>
%H Michael Somos, <a href="/A073189/a073189.txt">Sequences used for indexing triangular or square arrays</a>
%e 0; 0; 0,1; 0,1; 0,1,2; 0,1,2; 0,1,2,3; 0,1,2,3; ...
%t With[{nn=10},Flatten[Table[{Range[0,n],Range[0,n]},{n,0,nn}]]] (* _Harvey P. Dale_, May 30 2015 *)
%o (PARI) {a(n) = (1 + 4*n - sqr( floor( sqrt( 1 + 4*n)))) \ 4}
%o (Haskell)
%o import Data.List (transpose)
%o a055087 n k = a055087_tabf !! n !! k
%o a055087_row n = a055087_tabf !! n
%o a055087_tabf = concat $ transpose [a002262_tabl, a002262_tabl]
%o a055087_list = concat a055087_tabf
%o -- _Reinhard Zumkeller_, Jul 14 2015
%Y Cf. A002262.
%K nonn,easy,tabf
%O 0,9
%A _Michael Somos_, Jun 13 2000
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