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A131800 Period 4: repeat [1, 2, 5, 6]. 5
1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6, 1, 2, 5, 6 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Terms of the simple continued fraction of 4/(3*sqrt(21)-11). - Paolo P. Lava, Aug 05 2009

Decimal expansion of 1256/9999. - Klaus Brockhaus, May 20 2010

LINKS

Table of n, a(n) for n=0..107.

Salvatore Gambino, Terne pitagoriche primitive

Index entries for linear recurrences with constant coefficients, signature (0,0,0,1).

FORMULA

a(n) = (7+(-1)^n+4*(-1)^(2*n+1-(-1)^n)/4)/2.

G.f.: (1+2*x+5*x^2+6*x^3)/((1-x)*(x+1)*(x^2+1)). - R. J. Mathar, Jan 13 2008

a(n) = (1/6)*{11*(n mod 4)+2*[(n+1) mod 4]-[(n+2) mod 4]+2*[(n+3) mod 4]}. - Paolo P. Lava, Jan 28 2008

a(n) = 7/2-(1-I)*I^n-1/2*(-1)^n-(1+I)*(-I)^n with I=sqrt(-1). - Paolo P. Lava, Jul 17 2008

a(n) = A000111(n+2) mod 10.

a(n) = 7/2-2*cos(Pi*n/2)-2*sin(Pi*n/2)-(-1)^n/2. - R. J. Mathar, Oct 08 2011

a(n) = a(n-4) for n>3. - Wesley Ivan Hurt, Jul 10 2016

MAPLE

seq(op([1, 2, 5, 6]), n=0..50); # Wesley Ivan Hurt, Jul 10 2016

MATHEMATICA

PadRight[{}, 100, {1, 2, 5, 6}] (* Wesley Ivan Hurt, Jul 10 2016 *)

PROG

(PARI) a(n)=[1, 2, 5, 6][n%4+1] \\ Charles R Greathouse IV, Oct 07 2015

(MAGMA) &cat [[1, 2, 5, 6]^^30]; // Wesley Ivan Hurt, Jul 10 2016

CROSSREFS

Cf. A000111, A178131 (decimal expansion of (11+3*sqrt(21))/17).

Sequence in context: A111987 A004650 A138279 * A086038 A200136 A134387

Adjacent sequences:  A131797 A131798 A131799 * A131801 A131802 A131803

KEYWORD

nonn,easy

AUTHOR

Salvatore Gambino (salvatore.gambino(AT)fastwebnet.it), Oct 04 2007

EXTENSIONS

More terms from R. J. Mathar, Jan 13 2008

STATUS

approved

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Last modified February 24 22:04 EST 2020. Contains 332216 sequences. (Running on oeis4.)