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A087628 Generalized Jacobsthal sequence. 1
1, 2, 2, 2, 10, 22, 22, 86, 170, 170, 682, 1366, 1366, 5462, 10922, 10922, 43690, 87382, 87382, 349526, 699050, 699050, 2796202, 5592406, 5592406, 22369622, 44739242, 44739242, 178956970, 357913942, 357913942, 1431655766, 2863311530 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..32.

Index entries for linear recurrences with constant coefficients, signature (0,0,7,0,0,8).

FORMULA

a(n)=sum{k=0..n, if (mod(k(n-k), 3)=0, comb(n, k), 0) }; a(n)=if (mod(n, 3)=0, A001045(n+1)-A001045(n), A001045(n+1)-(-1)^n).

G.f.: ( -1-2*x-2*x^2+5*x^3+4*x^4-8*x^5 ) / ( (2*x-1)*(1+x)*(4*x^2+2*x+1)*(x^2-x+1) ). - R. J. Mathar, Dec 10 2014

CROSSREFS

Cf. A087629.

Sequence in context: A254706 A291666 A122946 * A263060 A089871 A236046

Adjacent sequences:  A087625 A087626 A087627 * A087629 A087630 A087631

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Sep 14 2003

STATUS

approved

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Last modified September 20 00:52 EDT 2020. Contains 337228 sequences. (Running on oeis4.)