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A145389
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Digital roots of triangular numbers.
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8
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0, 1, 3, 6, 1, 6, 3, 1, 9, 9, 1, 3, 6, 1, 6, 3, 1, 9, 9, 1, 3, 6, 1, 6, 3, 1, 9, 9, 1, 3, 6, 1, 6, 3, 1, 9, 9, 1, 3, 6, 1, 6, 3, 1, 9, 9, 1, 3, 6, 1, 6, 3, 1, 9, 9, 1, 3, 6, 1, 6, 3, 1, 9, 9, 1, 3, 6, 1, 6, 3, 1, 9, 9, 1, 3, 6, 1, 6, 3, 1, 9, 9, 1, 3, 6, 1, 6
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OFFSET
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0,3
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COMMENTS
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LINKS
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FORMULA
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Periodic sequence for n>0: a(n+9) = a(n);
a(n) = 1 + ((n^2 + n - 2)/2) mod 9. - Ant King, Apr 25 2009
G.f.: x(1 + 3x + 6x^2 + x^3 + 6x^4 + 3x^5 + x^6 + 9x^7 + 9x^8)/((1-x)(1 + x + x^2)(1 + x^3 + x^6)). - Ant King, Nov 16 2010
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MATHEMATICA
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digitalRoot[n_Integer?Positive] := FixedPoint[Plus@@IntegerDigits[#]&, n]; Table[If[n==0, 0, digitalRoot[n(n+1)/2]], {n, 0, 100}] (* Vladimir Joseph Stephan Orlovsky, May 02 2011 *)
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PROG
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(Python)
def A145389(n): return (9, 1, 3, 6, 1, 6, 3, 1, 9)[n%9] if n else 0 # Chai Wah Wu, Feb 09 2023
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CROSSREFS
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KEYWORD
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nonn,base,easy
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AUTHOR
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STATUS
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approved
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