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 A166925 Digital root of square of n-th triangular number. 1
 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9, 1, 9, 9 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Period is (1,9,9). LINKS Table of n, a(n) for n=1..87. Index entries for linear recurrences with constant coefficients, signature (0,0,1). FORMULA G.f.: x*(1+9*x+9*x^2)/(1-x^3). - Bruno Berselli, May 05 2011 a(n) = A010888(A000537(n)). - Michel Marcus, Mar 17 2023 MATHEMATICA Table[If[(m9 = Mod[(n(n + 1))^2/4, 9]) == 0, 9, m9], {n, 200}] PROG (Magma) &cat[[1, 9, 9]: n in [1..29]]; // Bruno Berselli, May 05 2011 CROSSREFS Cf. A000217, A000537, A010888. Sequence in context: A145280 A144667 A118428 * A178164 A216035 A171487 Adjacent sequences: A166922 A166923 A166924 * A166926 A166927 A166928 KEYWORD base,less,easy,nonn AUTHOR Zak Seidov, Oct 23 2009 STATUS approved

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Last modified July 20 17:32 EDT 2024. Contains 374459 sequences. (Running on oeis4.)