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A046192 Octagonal hexagonal numbers. 3
1, 11781, 113123361, 1086210502741, 10429793134197921, 100146872588357936901, 961610260163619775927681, 9233381617944204500099658261, 88658929333889991446337142696641 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

As n increases, this sequence is approximately geometric with common ratio r = lim(n->Infinity,a(n)/a(n-1)) = (sqrt(3)+sqrt(2))^8 = 4801+1960*sqrt(6).  - Ant King, Dec 27 2011

LINKS

Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 19 2008, Table of n, a(n) for n = 1..20

Eric Weisstein's World of Mathematics, Octagonal Hexagonal Number.

Index to sequences with linear recurrences with constant coefficients, signature (9603,-9603,1).

FORMULA

Contribution from Ant King, Dec 27 2011: (Start)

G.f.: x*(1+2178*x+21*x^2)/((1-x)*(1-9602*x+x^2)).

a(n) = 9603*a(n-1)-9603*a(n-2)+a(n-3).

a(n) = 9602*a(n-1)-a(n-2)+2200.

a(n) = 1/96*((3*sqrt(3)-sqrt(2))*(sqrt(3)+sqrt(2))^(8n-5)+ (3*sqrt(3)+sqrt(2))*(sqrt(3)-sqrt(2))^(8n-5)-22).

a(n) = floor(1/96*(3*sqrt(3)-sqrt(2))*(sqrt(3)+sqrt(2))^(8n-5)).

(End)

MAPLE

a:=5+2*sqrt(6): b:=5-2*sqrt(6): s:=n->a^n+b^n: d:=n->sqrt(6)*(a^n-b^n):for n from 0 to 40 do x:=simplify(s(n)-1/4*d(n)): y:=simplify(1/3*d(n)-s(n)/2): if(type((1+x/2)/3, integer) and type((1+y)/4, integer)) then printf("%d, ", (y^2-1)/8) fi: x:=simplify(s(n+1)+1/4*d(n+1)): y:=simplify(1/3*d(n+1)+s(n+1)/2): if(type((1+x/2)/3, integer) and type((1+y)/4, integer)) then printf("%d, ", (y^2-1)/8) fi: od: - Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 19 2008

MATHEMATICA

LinearRecurrence[{9603, -9603, 1}, {1, 11781, 113123361}, 9] (* Ant King, Dec 27 2011 *)

CROSSREFS

Cf. A046190, A046191.

Sequence in context: A045307 A229411 A235316 * A210151 A031868 A205630

Adjacent sequences:  A046189 A046190 A046191 * A046193 A046194 A046195

KEYWORD

nonn,easy

AUTHOR

Eric W. Weisstein

EXTENSIONS

More terms from Larry Reeves (larryr(AT)acm.org), May 07 2001

One more term from Lior Manor Feb 13 2002

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 19 2008

STATUS

approved

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Last modified April 23 12:03 EDT 2014. Contains 240919 sequences.