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A122995 Expansion of x*(1+4*x)/(1-x-25*x^2). 6
1, 5, 30, 155, 905, 4780, 27405, 146905, 832030, 4504655, 25305405, 137921780, 770556905, 4218601405, 23482524030, 128947559155, 716010659905, 3939699638780, 21839966136405, 120332457105905, 666331610516030, 3674643038163655, 20332933301064405, 112199009255155780 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The sequence can also be generated by adding of the top-row elements of the (n-1)st power of the matrix [[0,1],[1,1/5]] and multiplying with 5^(n-1).

LINKS

Nathaniel Johnston, Table of n, a(n) for n = 1..500

Index entries for linear recurrences with constant coefficients, signature (1,25)

FORMULA

a(n) = a(n-1)+25*a(n-2). [Philippe Deléham, Mar 26 2009]

a(n) = A122999(n-1) + 4*A122999(n-2). [R. J. Mathar, Aug 12 2009]

a(n) = (1/2+9*sqrt(101)/202)*(1/2+sqrt(101)/2)^(n-1) + (1/2-9*sqrt(101)/202)*(1/2-sqrt(101)/2)^(n-1). [Antonio Alberto Olivares, Jun 07 2011]

MATHEMATICA

M := {{0, 1}, {1, 1/5}}; v[1] = {1, 1}; v[n_] := v[n] = M.v[n - 1]; a = Table[v[n][[1]]*5^(n - 1), {n, 1, 30}]

LinearRecurrence[{1, 25}, {1, 5}, 30] (* Harvey P. Dale, Mar 11 2017 *)

PROG

(PARI) Vec(x*(1+4*x)/(1-x-25*x^2) + O(x^30)) \\ Michel Marcus, Jan 28 2015

CROSSREFS

Cf. A026597.

Sequence in context: A104891 A246937 A110155 * A254944 A003731 A343362

Adjacent sequences: A122992 A122993 A122994 * A122996 A122997 A122998

KEYWORD

nonn,easy

AUTHOR

Roger L. Bagula, Sep 22 2006

EXTENSIONS

Replaced definition by a specific one - The Assoc. Eds. of the OEIS, Jun 07 2010

More terms from Michel Marcus, Jan 28 2015

STATUS

approved

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Last modified December 4 16:41 EST 2022. Contains 358563 sequences. (Running on oeis4.)