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%I #5 Jun 05 2013 14:39:15
%S 0,0,1,2,3,4,0,1,2,3,4,5,6,7,8,0,1,2,3,4,5,6,7,8,9,10,11,12,0,1,2,3,4,
%T 5,6,7,8,9,10,11,12,13,14,15,16,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,
%U 16,17,18,19,20,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20
%N Hexagonal excess: smallest amount by which n exceeds a hexagonal number (2k^2-k, A000384).
%e a(19)=4 since 15(=2*3^2-3) is the largest hexagonal less than or equal to 19 and 19-15=4.
%t Flatten[Range[#]&/@Differences[Array[#(2#-1)&,10,0]]-1] (* _Harvey P. Dale_, Jun 05 2013 *)
%Y Cf. A002262, A053186, A055400, A060510.
%K easy,nonn
%O 0,4
%A _Henry Bottomley_, Mar 22 2001