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 A068131 Triangular numbers with sum of digits = 21. 3
 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, 57630 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS 1. The sequence is unbounded, as the (5*10^k + 6)-th triangular number is a term. 2. The sum of the digits of triangular numbers in most cases is a triangular number. 3. Conjecture: For every triangular number T there exist infinitely many triangular numbers with sum of digits = T. LINKS Harvey P. Dale, Table of n, a(n) for n = 0..1000 MATHEMATICA Select[Accumulate[Range[400]], Total[IntegerDigits[#]]==21&] (* Harvey P. Dale, Jun 06 2015 *) CROSSREFS Cf. A068127, A068128, A068129, A068130. Sequence in context: A224946 A316335 A179248 * A068263 A078954 A117745 Adjacent sequences:  A068128 A068129 A068130 * A068132 A068133 A068134 KEYWORD base,easy,nonn AUTHOR Amarnath Murthy, Feb 21 2002 EXTENSIONS More terms from Sascha Kurz, Mar 06 2002 STATUS approved

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Last modified October 14 00:31 EDT 2019. Contains 327991 sequences. (Running on oeis4.)