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A048921 9-gonal heptagonal numbers (A000566). 2
1, 26884, 542041975, 10928650279834, 220343446399977901, 4442564555387704166896, 89570986345383445012986019, 1805930222253056462964119954950, 36411165051495138060899141518722649 (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)) = (6+sqrt(35))^4 = 10081+1704*sqrt(35).  - Ant King, Dec 31 2011

LINKS

Table of n, a(n) for n=1..9.

Eric Weisstein's World of Mathematics, Nonagonal Heptagonal Number.

FORMULA

Contribution from Ant King, Dec 31 2011: (Start)

a(n) = 20163*a(n-1)-20163*a(n-2)+a(n-3).

a(n) = 20162*a(n-1)-a(n-2)+6768.

a(n) = 1/560*((39+4*sqrt(35))*(6+sqrt(35))^(4*n-3)+(39-4*sqrt(35))*(6-sqrt(35))^(4*n-3)-188).

a(n) = floor(1/560*(39+4*sqrt(35))*(6+sqrt(35))^(4*n-3)).

G.f.: x(1+6721*x+46*x^2) / ((1-x)(1-20162*x+x^2)).

(End)

MATHEMATICA

LinearRecurrence[{20163, -20163, 1}, {1, 26884, 542041975}, 9]; (* Ant King, Dec 31 2011 *)

CROSSREFS

Cf. A048919, A048920.

Sequence in context: A235814 A199547 A051025 * A249496 A227348 A176359

Adjacent sequences:  A048918 A048919 A048920 * A048922 A048923 A048924

KEYWORD

nonn

AUTHOR

Eric W. Weisstein

STATUS

approved

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Last modified November 23 16:16 EST 2014. Contains 249851 sequences.