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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
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
Sequence in context: A145280 A144667 A118428 * A178164 A216035 A171487
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.)