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 A008621 Expansion of 1/((1-x)*(1-x^4)). 21
 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 10, 11, 11, 11, 11, 12, 12, 12, 12, 13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 19, 19, 19, 19, 20, 20, 20, 20, 21, 21 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS Arises from Gleason's theorem on self-dual codes: 1/((1-x^2)*(1-x^8)) is the Molien series for the real 2-dimensional Clifford group (a dihedral group of order 16) of genus 1. Count of odd numbers between consecutive quarter-squares, A002620. Oppermann's conjecture states that for each count there will be at least one prime. - Fred Daniel Kline, Sep 10 2011 Number of partitions into parts 1 and 4. - Joerg Arndt, Jun 01 2013 REFERENCES D. J. Benson, Polynomial Invariants of Finite Groups, Cambridge, 1993, p. 100. F. J. MacWilliams and N. J. A. Sloane, Theory of Error-Correcting Codes, 1977, Chapter 19, Problem 3, p. 602. LINKS T. D. Noe, Table of n, a(n) for n = 0..1000 INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 211 G. Nebe, E. M. Rains and N. J. A. Sloane, Self-Dual Codes and Invariant Theory, Springer, Berlin, 2006. Wikipedia, Oppermann's Conjecture Index entries for linear recurrences with constant coefficients, signature (1,0,0,1,-1). FORMULA a(n) = floor(n/4) + 1. a(n) = A010766(n+4, 4). a(n) = {Sum{k=0..n, (k+1)cos(pi*(n-k)/2}+1/4[cos(n*Pi/2)+1+(-1)^n] }/2 - Paolo P. Lava, Oct 09 2006 Also, a(n) = ceiling((n+1)/4), n >= 0. - Mohammad K. Azarian, May 22 2007 a(n) = Sum_{i=0..n} A121262(i) = n/4 +5/8 +(-1)^n/8 + A057077(n)/4. - R. J. Mathar, Mar 14 2011 a(x,y):= floor(x/2) + floor(y/2) - x where x=A002620(n) and y=A002620(n+1), n>2. - Fred Daniel Kline, Sep 10 2011 a(0)=1, a(1)=1, a(2)=1, a(3)=1, a(4)=2, a(n) = a(n-1) + a(n-4) - a(n-5). - Harvey P. Dale, Feb 19 2012 MATHEMATICA Table[Floor[n/4]+1, {n, 0, 80}] (* Stefan Steinerberger, Apr 03 2006 *) CoefficientList[Series[1/((1-x)(1-x^4)), {x, 0, 80}], x] (* Harvey P. Dale, Feb 19 2012 *) Flatten[ Table[ PadRight[{}, 4, n], {n, 19}]] (* Harvey P. Dale, Feb 19 2012 *) PROG (PARI) a(n)=n\4+1 \\ Charles R Greathouse IV, Feb 06 2017 CROSSREFS Cf. A008718, A024186, A110160, A110868, A110869, A110876, A110880, A002265, A008620. Sequence in context: A002265 A242601 A110655 * A144075 A128929 A257839 Adjacent sequences:  A008618 A008619 A008620 * A008622 A008623 A008624 KEYWORD nonn,easy,nice AUTHOR EXTENSIONS More terms from Stefan Steinerberger, Apr 03 2006 STATUS approved

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Last modified November 22 03:41 EST 2019. Contains 329387 sequences. (Running on oeis4.)