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A048900 Heptagonal pentagonal numbers. 2
1, 4347, 16701685, 64167869935, 246532939589097, 947179489733441251, 3639063353022941697757, 13981280455134652269341655, 53716075869563980995868941265, 206377149509584359851476202998987 (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))=(4+sqrt(15))^4=1921+496*sqrt(15). - Ant King, Dec 15 2011

LINKS

Table of n, a(n) for n=1..10.

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

FORMULA

From Ant King, Dec 15 2011: (Start)

a(n) = 3843*a(n-1) - 3843*a(n-2) + a(n-3).

a(n) = 3842*a(n-1) - a(n-2) + 512.

a(n) = 1/240*((2+sqrt(15))^2*(4+sqrt(15))^(4n-3)+ (2-sqrt(15))^2*(4-sqrt(15))^(4n-3)-32).

a(n) = floor(1/240*((2+sqrt(15))^2*(4+sqrt(15))^(4n-3))).

GF: x*(1+504*x+7*x^2)/((1-x)*(1-3842*x+x^2)).

(End)

MATHEMATICA

LinearRecurrence[{3843, -3843, 1}, {1, 4347, 16701685}, 10] (* Ant King, Dec 15 2011 *)

CROSSREFS

Cf. A046198, A046199.

Sequence in context: A172884 A172915 A145916 * A235066 A170786 A223378

Adjacent sequences:  A048897 A048898 A048899 * A048901 A048902 A048903

KEYWORD

nonn,easy

AUTHOR

Eric W. Weisstein

STATUS

approved

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Last modified September 20 07:38 EDT 2014. Contains 246994 sequences.