A117309 Triangular numbers for which the sum of the digits is a hexagonal number.

0, 1, 6, 10, 15, 78, 105, 231, 276, 465, 528, 780, 861, 1176, 1275, 1653, 1770, 2211, 2346, 2850, 3003, 3570, 3741, 4371, 4560, 5253, 5460, 5995, 6216, 6441, 7260, 7503, 11175, 12246, 12561, 14028, 14878, 15225, 17205, 17578, 20301, 20706, 22155, 24090

Offset

0,3

Links

Harvey P. Dale, Table of n, a(n) for n = 0..1000

Example

105 is in the sequence because (1) it is a triangular number and (2) the sum of its digits 1+0+5=6 is a hexagonal number.

Mathematica

Join[{0}, Select[Accumulate[Range[350]], IntegerQ[(1+Sqrt[8Total[ IntegerDigits[#]]+1])/4]&]] (* Harvey P. Dale, Jun 06 2011 *)

Crossrefs

Cf. A000217, A000384.

Sequence in context: A048078 A229276 A319035 * A228300 A342480 A299996

Adjacent sequences: A117306 A117307 A117308 * A117310 A117311 A117312

Keyword

base,nonn

Author

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

Extensions

Corrected and extended by Harvey P. Dale, Jun 06 2011

Status

approved