A117404 Triangular numbers for which the sum of the digits is a square.

0, 1, 10, 36, 45, 153, 171, 351, 630, 1035, 1431, 2016, 3240, 3321, 4005, 8001, 10440, 13041, 13203, 16110, 21321, 23220, 25200, 67896, 89676, 101025, 105111, 114003, 186966, 187578, 198765, 222111, 239778, 279378, 292995, 299925, 320400, 321201

Offset: 1

Author

Luc Stevens (lms022(AT)yahoo.com), Apr 26 2006

Keywords

• base
• nonn

Examples

			45 is in the sequence because (1) it is a triangular number and (2) the sum of its digits 4+5=9 is a square.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000217.

Programs

Mathematica

Select[Accumulate[Range[0,1000]],IntegerQ[Sqrt[Total[IntegerDigits[ #]]]]&] (* Harvey P. Dale, Dec 26 2014 *)

PARI

isok(n) = ispolygonal(n, 3) && issquare(sumdigits(n)); \\ Michel Marcus, Feb 26 2014

Extensions

Corrected by Michel Marcus, Feb 26 2014