A117523 Triangular numbers for which the sum of the digits is an octagonal number.

0, 1, 10, 1596, 2775, 3486, 3828, 4278, 4656, 5565, 6555, 7626, 8256, 9453, 14196, 15753, 16653, 17391, 18336, 21945, 22791, 23871, 24753, 28920, 32385, 34716, 37128, 38226, 39621, 40755, 42195, 43365, 44850, 46056, 51681, 54615, 56280

Offset

1,3

Links

Michael De Vlieger, Table of n, a(n) for n = 1..3618

Example

1596 is in the sequence because (1) it is a triangular number and (2) the sum of its digits 1+5+9+6=21 is a octagonal number.

Mathematica

Join[{0}, Select[Accumulate[Range[400]], IntegerQ[(1+Sqrt[1+3*Total[ IntegerDigits[ #]]])/3]&]] (* Harvey P. Dale, May 06 2019 *)

Prog

(PARI) isok(n) = ispolygonal(n, 3) && ispolygonal(sumdigits(n), 8); \\ Michel Marcus, Feb 26 2014

Crossrefs

Cf. A000217, A000567.

Sequence in context: A286397 A160236 A204466 * A203696 A203530 A232594

Adjacent sequences: A117520 A117521 A117522 * A117524 A117525 A117526

Keyword

base,nonn

Author

Luc Stevens (lms022(AT)yahoo.com), Apr 30 2006

Status

approved