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A185273
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Period 6: repeat [1, 6, 5, 6, 1, 0].
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1
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1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6, 5, 6, 1, 0, 1, 6
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OFFSET
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1,2
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COMMENTS
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The terms of this sequence are the units' digits of the nonzero square triangular numbers.
The coefficients of x in the numerator of the generating function are the terms that constitute the periodic cycle of the sequence.
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LINKS
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FORMULA
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G.f.: x*(1+6*x+5*x^2+6*x^3+x^4) / ((1-x)*(1+x)*(1-x+x^2)*(1+x+x^2)).
a(n) = a(n-6) for n>6.
a(n) = 19 - a(n-1) - a(n-2) - a(n-3) - a(n-4) - a(n-5) for n>5.
a(n) = (1/3)*(sin(n*Pi/6))^2*(57+76*cos(n*Pi/3)+58*cos(2*n*Pi/3)+44*cos(n*Pi)+20*cos(4*n*Pi/3)).
a(n) = (1/45)*(17*(n mod 6)+47*((n+1) mod 6)+2*((n+2) mod 6)+17*((n+3) mod 6)-28*((n+4) mod 6)+2*((n+5) mod 6)). - Bruno Berselli, Jan 24 2012
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EXAMPLE
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The fourth nonzero square triangular number is 41616. As this has units' digit 6, we have a(4) = 6.
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MAPLE
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MATHEMATICA
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LinearRecurrence[{0, 0, 0, 0, 0, 1}, {1, 6, 5, 6, 1, 0}, 86]
PadRight[{}, 120, {1, 6, 5, 6, 1, 0}] (* Harvey P. Dale, Sep 22 2015 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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