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%I #18 Apr 09 2016 03:20:30
%S 0,0,1,0,2,3,0,4,5,6,0,7,8,9,10,0,11,12,13,14,15,0,16,17,18,19,20,21,
%T 0,22,23,24,25,26,27,28,0,29,30,31,32,33,34,35,36,0,37,38,39,40,41,42,
%U 43,44,45,0,46,47,48,49,50,51,52,53,54,55,0,56,57,58
%N If n is a triangular number, a(n) = 0, otherwise a(n) = n - A002024(n) + 1
%C a(n) gives the number above n when the natural numbers are represented as a square array, or 0 if n is in the top row.
%C 1 3 6 10
%C 2 5 9
%C 4 8
%C 7
%H Peter Kagey, <a href="/A271439/b271439.txt">Table of n, a(n) for n = 0..10000</a>
%e As a regular triangle, sequence begins:
%e 0;
%e 0, 1;
%e 0, 2, 3;
%e 0, 4, 5, 6;
%e 0, 7, 8, 9, 10;
%e ...
%t Riffle[#, 0] &@ Map[# (# - 1)/2 + Range@ # &, Range[0, 11]] /. {} -> {0} // Flatten (* _Michael De Vlieger_, Apr 07 2016 *)
%Y Cf. A000217 (right diagonal), A006003 (row sums).
%K nonn,tabl
%O 0,5
%A _Peter Kagey_, Apr 07 2016
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