A117312 Triangular numbers for which the sum of the digits is a heptagonal number.

0, 1, 10, 378, 666, 990, 1485, 1953, 2556, 2628, 4095, 4851, 4950, 6903, 9045, 9180, 10296, 11628, 11781, 14535, 14706, 16290, 19503, 19701, 21528, 23436, 25425, 27261, 29403, 31626, 33930, 34191, 36315, 39060, 41328, 41616, 44253, 52326

Offset

0,3

Links

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

Example

378 is in the sequence because (1) it is a triangular number and (2) the sum of its digits 3+7+8=18 is a heptagonal number.

Mathematica

Join[{0}, Select[Accumulate[Range[0, 500]], IntegerQ[(3+Sqrt[40*Total[ IntegerDigits[ #]]+9])/10]&]] (* Harvey P. Dale, Aug 10 2013 *)

Crossrefs

Cf. A000217, A000566.

Sequence in context: A301311 A291530 A358801 * A200804 A277663 A000591

Adjacent sequences: A117309 A117310 A117311 * A117313 A117314 A117315

Keyword

base,nonn

Author

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

Status

approved