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 A143025 Period length 4: repeat [1, 8, 2, 8]. 5
 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Numerator of 1/n^2-1/(3n)^2 if n>0. This can be generated from the transitions between principal quantum numbers n and 3n in the Hydrogen series: A005563(2), A061037(6), A061039(9), A061041(12), A061043(15), A061045(18), A061047(21), A061049(24),... (The mention of A005563(2) is somewhat a fluke to maintain the periodic pattern.) Related to the continued fraction of (12*sqrt(55)-72)/19 = 0.89444115.. = 0+1/(1+1/(8+1/(2+...))). - R. J. Mathar, Jun 27 2011 LINKS Index entries for linear recurrences with constant coefficients, signature (0,0,0,1). FORMULA a(n+4) = a(n). a(n) = (1/24)*(61*(n mod 4)-17*((n+1) mod 4)+55*((n+2) mod 4)-23*((n+3) mod 4)). [Paolo P. Lava, Feb 23 2010] G.f.: (1+8*x+2*x^2+8*x^3)/(1-x^4). From Wesley Ivan Hurt, Jul 10 2016: (Start) a(n) = (19 - 13*I^(2*n) - I^(-n) - I^n)/4, where I = sqrt(-1). a(n) = (19 - 2*cos(n*Pi/2) - 13*cos(n*Pi))/4. (End) MAPLE seq(op([1, 8, 2, 8]), n=0..50); # Wesley Ivan Hurt, Jul 10 2016 MATHEMATICA PadRight[{}, 120, {1, 8, 2, 8}] (* Harvey P. Dale, Jul 01 2015 *) PROG (PARI) a(n)=[1, 8, 2, 8][n%4+1] \\ Charles R Greathouse IV, Jun 02 2011 (MAGMA) &cat [[1, 8, 2, 8]^^30]; // Wesley Ivan Hurt, Jul 10 2016 CROSSREFS Cf. A045944, A144437. Sequence in context: A248299 A253721 A021551 * A303326 A085967 A163960 Adjacent sequences:  A143022 A143023 A143024 * A143026 A143027 A143028 KEYWORD nonn,easy AUTHOR Paul Curtz, Oct 13 2008 EXTENSIONS Partially edited by R. J. Mathar, Dec 10 2008 STATUS approved

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Last modified July 30 19:12 EDT 2021. Contains 346359 sequences. (Running on oeis4.)