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A048903 Heptagonal hexagonal numbers. 2
1, 121771, 12625478965, 1309034909945503, 135723357520344181225, 14072069153115290487843091, 1459020273797576190840203197981, 151274140013808225465578657485241095 (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)) = (2+sqrt(5))^8 = 51841+23184*sqrt(5).  - Ant King, Dec 24 2011

LINKS

Table of n, a(n) for n=1..8.

Eric Weisstein's World of Mathematics, Heptagonal Hexagonal Number

Index to sequences with linear recurrences with constant coefficients, signature (103683,-103683,1).

FORMULA

Contribution from Ant King, Dec 24 2011: (Start)

G.f.: x*(1+18088*x+55*x^2)/((1-x)*(1-103682*x+x^2)).

a(n) = 103683*a(n-1)-103683*a(n-2)+a(n-3).

a(n) = 103682*a(n-1)-a(n-2)+18144.

a(n) = 1/80*((sqrt(5)-1)*(2+sqrt(5))^(8n-5)- (sqrt(5)+1)*(2-sqrt(5))^(8n-5)-14).

a(n) = floor(1/80*(sqrt(5)-1)*(2+sqrt(5))^(8n-5)).

(End)

MATHEMATICA

LinearRecurrence[{103683, -103683, 1}, {1, 121771, 12625478965}, 8]; (* Ant King, Dec 24 2011 *)

CROSSREFS

Cf. A048901, A048902.

Sequence in context: A135495 A067384 A066881 * A237793 A185864 A236797

Adjacent sequences:  A048900 A048901 A048902 * A048904 A048905 A048906

KEYWORD

nonn,easy

AUTHOR

Eric W. Weisstein

STATUS

approved

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Last modified October 31 03:51 EDT 2014. Contains 248845 sequences.