

A001638


A Fielder sequence: a(n) = a(n1) + a(n3) + a(n4), n >= 4.
(Formerly M3351 N1348)


9



4, 1, 1, 4, 9, 11, 16, 29, 49, 76, 121, 199, 324, 521, 841, 1364, 2209, 3571, 5776, 9349, 15129, 24476, 39601, 64079, 103684, 167761, 271441, 439204, 710649, 1149851, 1860496, 3010349, 4870849, 7881196, 12752041, 20633239, 33385284, 54018521, 87403801
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OFFSET

0,1


COMMENTS

For n > 1, a(n) is the number of ways of choosing a subset of vertices of an ncycle so that every vertex of the ncycle is adjacent to one of the chosen vertices. (Note that this is not the same as the number of dominating sets of the ncycle, which is given by A001644.)  Joel B. Lewis, Sep 12 2010


REFERENCES

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

T. D. Noe, Table of n, a(n) for n = 0..1000
Daniel C. Fielder, Special integer sequences controlled by three parameters, Fibonacci Quarterly 6, 1968, 6470.
Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992.
Simon Plouffe, 1031 Generating Functions and Conjectures, Université du Québec à Montréal, 1992.
Middle European Math Olympiad 2010, Team Problem 3. Available online at the Art of Problem Solving. [From Joel B. Lewis, Sep 12 2010]
Index entries for linear recurrences with constant coefficients, signature (1, 0, 1, 1).


FORMULA

G.f.: (1x)(4+x+x^2)/((1+x^2)(1xx^2)).
a(n) = L(n) + i^n + (i)^n, a(2n) = L(n)^2, a(2n+1) = L(2n+1) where L() is Lucas sequence.


MAPLE

A001638:=(z+1)*(4*z**2z+1)/(z**2+z1)/(z**2+1); # conjectured by Simon Plouffe in his 1992 dissertation; gives sequence except for the initial 4


MATHEMATICA

LinearRecurrence[{1, 0, 1, 1}, {4, 1, 1, 4}, 50] (* T. D. Noe, Aug 09 2012 *)


PROG

(PARI) a(n)=if(n<0, 0, fibonacci(n+1)+fibonacci(n1)+simplify(I^n+(I)^n))
(PARI) a(n)=if(n<0, 0, polsym((1+xx^2)*(1+x^2), n)[n+1])


CROSSREFS

Sequence in context: A209571 A269845 A124258 * A133826 A209565 A122185
Adjacent sequences: A001635 A001636 A001637 * A001639 A001640 A001641


KEYWORD

nonn


AUTHOR

N. J. A. Sloane


EXTENSIONS

Edited by Michael Somos, Feb 17 2002 and Nov 02 2002


STATUS

approved



