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A117523
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Triangular numbers for which the sum of the digits is an octagonal number.
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1
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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
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OFFSET
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1,3
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LINKS
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EXAMPLE
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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.
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MATHEMATICA
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Join[{0}, Select[Accumulate[Range[400]], IntegerQ[(1+Sqrt[1+3*Total[ IntegerDigits[ #]]])/3]&]] (* Harvey P. Dale, May 06 2019 *)
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PROG
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(PARI) isok(n) = ispolygonal(n, 3) && ispolygonal(sumdigits(n), 8); \\ Michel Marcus, Feb 26 2014
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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Luc Stevens (lms022(AT)yahoo.com), Apr 30 2006
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STATUS
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approved
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