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A080891
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Period 5: repeat [0, 1, -1, -1, 1].
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42
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0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0, 1, -1, -1, 1, 0
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OFFSET
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0,1
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COMMENTS
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a(n) = (5/n), where (k/n) is the Kronecker symbol.
L(1;5) (Dirichlet L-series) is the integral from 0 to 1 of the g.f. of a(n+1). Partial sums are A092202. - Paul Barry, Apr 01 2005
From R. J. Mathar, Jul 15 2010, simplified Jul 27 2010: (Start)
The sequence is the real non-principal Dirichlet character mod 5 (The principal character mod 5 is A011558.)
Associated Dirichlet L-functions are for example L(1,chi) = sum_{n>=1} a(n)/n = A086466 or L(2,chi)= sum_{n>=1} a(n)/n^2 = 0.7062114... = 4*Pi^2/(25*sqrt(5)). (End)
This sequence a(n) appears in the formula 2*exp(2*Pi*n*I/5) = (A(n) + a(n)*phi) + (C(n) + D(n)*phi)*sqrt(2 + phi)*I, with the golden section phi, I = sqrt(-1) and A(n) = A164116(n+5), C(n) = A156174(n+4) and D(n) = A010891(n+3) for n >= 0. See a comment on A164116. - Wolfdieter Lang, Feb 26 2014
In Gil and Robins 2003 on page 33 the g.f. is denoted by f_{4, 4}(x). - Michael Somos, Sep 04 2015
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REFERENCES
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T. M. Apostol, Introduction to Analytic Number Theory, Springer-Verlag, 1986, page 139, k=5, Chi_2(n).
H. Cohn, Advanced Number Theory, Dover Publications, Inc., 1962, p. 173.
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LINKS
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FORMULA
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If n==0 (mod 5) a(n)=0; if n==1 or 4 (mod 5) a(n)=1; if n==2 or 3 (mod 5) a(n)=-1.
G.f.: x*(1-x^2)/(1+x+x^2+x^3+x^4). - Paul Barry, Apr 01 2005
G.f.: x * (1 - x) * (1 - x^2) / (1 - x^5). a(n) = a(-n) = a(n+5) for all n in Z. - Michael Somos, Jun 17 2005
Euler transform of length 5 sequence [-1, -1, 0, 0, 1]. - Michael Somos, Jun 17 2005
Transform of the Fibonacci numbers by the Riordan array A102587. - Paul Barry, Jul 14 2005
a(n) is completely multiplicative with a(p) = Kronecker( 5, p). - Michael Somos, Jun 17 2015
a(n) = a(n-5) for n > 4.
a(n) + a(n-1) + a(n-2) + a(n-3) + a(n-4) = 0 for n > 3.
a(n) = 1 + 2*floor((n-4)/5) - 2*floor((n-2)/5) + floor((n-1)/5) - floor(n/5). (End)
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EXAMPLE
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G.f. = x - x^2 - x^3 + x^4 + x^6 - x^7 - x^8 + x^9 + x^11 - x^12 - x^13 + ...
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MAPLE
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MATHEMATICA
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a[ n_] := KroneckerSymbol[ n, 5]; (* Michael Somos, May 24 2015 *)
a[ n_] := {1, -1, -1, 1, 0}[[Mod[n, 5, 1]]]; (* Michael Somos, May 24 2015 *)
PadRight[{}, 120, {0, 1, -1, -1, 1}] (* Harvey P. Dale, Nov 30 2023 *)
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PROG
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(PARI) a(n)=kronecker(5, n) /* Also, a(n)=kronecker(n, 5) */
(PARI) {a(n) = (n^2 + 1)%5 - 1}; /* Michael Somos, Dec 01 2004 */
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CROSSREFS
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KEYWORD
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sign,mult,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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