A068898 - OEIS

%I #9 Sep 21 2024 17:36:44

%S 55,66,2415,3003,5050,5151,5995,8778,9045,113050,138075,171405,174345,

%T 177906,183921,198765,203203,216153,219453,234270,237705,239086,

%U 252405,255255,266815,267546,275653,279378,284635,293761,294528,306153,309291,329266,348195

%N Triangular numbers containing 2k digits in which the sum of the first k digits = that of the rest.

%H Harvey P. Dale, <a href="/A068898/b068898.txt">Table of n, a(n) for n = 1..1000</a>

%e 2415 is a term with 2+4 = 1+5.

%t dsQ[n_]:=Module[{idn=IntegerDigits[n],len=IntegerLength[n]/2}, Total[Take[ idn,len]] ==Total[ Take[idn,-len]]]; Select[Flatten[ Table[Table[(n(n+1))/2,{n,Ceiling[(Sqrt[8 10^i+1]-1)/2],Floor[ (Sqrt[8 10^(i+1)+1]-1)/2]}],{i,1,5,2}]],dsQ] (* _Harvey P. Dale_, Sep 29 2011 *)

%Y Intersection of A000217 and A240927.

%Y Cf. A068896, A068897.

%K easy,nonn,base

%O 1,1

%A _Amarnath Murthy_, Mar 21 2002

%E Corrected and extended by _Harvey P. Dale_, Sep 29 2011

%E Offset changed by _Andrew Howroyd_, Sep 21 2024