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A117523
Triangular numbers for which the sum of the digits is an octagonal number.
1
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
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 an 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
Sequence in context: A286397 A160236 A204466 * A203696 A203530 A232594
KEYWORD
base,nonn
AUTHOR
Luc Stevens (lms022(AT)yahoo.com), Apr 30 2006
STATUS
approved