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A154597 a(n) = 15*a(n-1) + a(n-2) with a(0)=0, a(1)=1. 9
1, 15, 226, 3405, 51301, 772920, 11645101, 175449435, 2643386626, 39826248825, 600037119001, 9040383033840, 136205782626601, 2052127122432855, 30918112619119426, 465823816409224245, 7018275358757483101 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Lim_{n -> infinity} a(n)/a(n-1) = 1/(imaginary part of (15+2*i)^(1/2))^2 = 15.0663729752..., where i=sqrt(-1). -Klaus Brockhaus, Oct 07 2009

For more information about this type of recurrence follow the Khovanova link and see A054413, A086902 and A178765. - Johannes W. Meijer, Jun 12 2010

For n>=2, a(n) equals the permanent of the (n-1) X (n-1) tridiagonal matrix with 15's along the main diagonal, and 1's along the superdiagonal and the subdiagonal. - John M. Campbell, Jul 08 2011

a(n) equals the number of words of length n-1 on alphabet {0,1,...,15} avoiding runs of zeros of odd lengths. - Milan Janjic, Jan 28 2015

LINKS

Table of n, a(n) for n=1..17.

Tanya Khovanova, Recursive sequences. [From Johannes W. Meijer, Jun 12 2010]

Index entries for linear recurrences with constant coefficients, signature (15, 1).

FORMULA

G.f.: x/(1-15*x-x^2). - Klaus Brockhaus, Jan 12 2009, corrected Oct 07 2009

a(n) = ((15 + sqrt(229))^n - (15 - sqrt(229))^n)/(2^n*sqrt(229)).

From Johannes W. Meijer, Jun 12 2010: (Start)

Limit(a(n+k)/a(k), k=infinity) = (A090301(n) + A154597(n)*sqrt(229))/2

Limit(A090301(n)/ A154597(n), n=infinity) = sqrt(229).

a(2n+1) = 15*A098245(n-1).

a(3n+1) = A041427(5n), a(3n+2) = A041427(5n+3), a(3n+3) = 2*A041427(5n+4). (End)

MATHEMATICA

a=0; lst={}; s=0; Do[a=s-(a-1); AppendTo[lst, a]; s+=a*15, {n, 3*4!}]; lst (* Vladimir Joseph Stephan Orlovsky, Oct 27 2009 *)

PROG

(MAGMA) Z<x>:=PolynomialRing(Integers()); N<r>:=NumberField(x^2-229); S:=[ ((15+r)^n-(15-r)^n)/(2^n*r): n in [1..17] ]; [ Integers()!S[j]: j in [1..#S] ]; // Klaus Brockhaus, Jan 12 2009

CROSSREFS

First bisection is A098247.

Cf. A166125 (decimal expansion of sqrt(229)), A166126 (decimal expansion of 1/(imaginary part of (15+2*i)^(1/2))^2).

Cf. A243399.

Sequence in context: A001024 A012643 A067222 * A041422 A129836 A075262

Adjacent sequences:  A154594 A154595 A154596 * A154598 A154599 A154600

KEYWORD

nonn,easy,changed

AUTHOR

Al Hakanson (hawkuu(AT)gmail.com), Jan 12 2009

EXTENSIONS

Extended beyond a(7) by Klaus Brockhaus and Philippe Deléham, Jan 12 2009

Name from Philippe Deléham, Jan 12 2009

Edited by Klaus Brockhaus, Oct 07 2009

STATUS

approved

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Last modified March 24 22:17 EDT 2017. Contains 284035 sequences.