A068898 Triangular numbers containing 2k digits in which the sum of the first k digits = that of the rest.

55, 66, 2415, 3003, 5050, 5151, 5995, 8778, 9045, 113050, 138075, 171405, 174345, 177906, 183921, 198765, 203203, 216153, 219453, 234270, 237705, 239086, 252405, 255255, 266815, 267546, 275653, 279378, 284635, 293761, 294528, 306153, 309291, 329266, 348195

Offset: 1

Author

Amarnath Murthy, Mar 21 2002

Keywords

• easy
• nonn
• base

Examples

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

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Intersection of A000217 and A240927.

Cf. A068896, A068897.

Programs

Mathematica

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 *)

Extensions

Corrected and extended by Harvey P. Dale, Sep 29 2011

Offset changed by Andrew Howroyd, Sep 21 2024