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A259161 Positive pentagonal numbers (A000326) that are triangular numbers (A000217) divided by 2. 3
5, 48510, 465793515, 4472549283020, 42945417749765025, 412361896760694487530, 3959498889750770719498535, 38019107927025003687930446040, 365059470355795195660737423378045, 3505300996337237541709397051345542550, 33657899801770684519698434826282476187555 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Colin Barker, Table of n, a(n) for n = 1..251

Index entries for linear recurrences with constant coefficients, signature (9603,-9603,1).

FORMULA

G.f.: -5*x*(99*x+1) / ((x-1)*(x^2-9602*x+1)).

EXAMPLE

5 is in the sequence because 5 is the 2nd pentagonal number, and 2*5 is the 4th triangular number.

MATHEMATICA

LinearRecurrence[{9603, -9603, 1}, {5, 48510, 465793515}, 20] (* Vincenzo Librandi, Jun 20 2015 *)

PROG

(PARI) Vec(-5*x*(99*x+1)/((x-1)*(x^2-9602*x+1)) + O(x^20))

CROSSREFS

Cf. A000217, A000326, A074378, A259156-A259160, A259162-A259167.

Sequence in context: A307492 A165711 A167369 * A242833 A242478 A247845

Adjacent sequences:  A259158 A259159 A259160 * A259162 A259163 A259164

KEYWORD

nonn,easy

AUTHOR

Colin Barker, Jun 19 2015

STATUS

approved

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Last modified August 18 09:28 EDT 2022. Contains 356204 sequences. (Running on oeis4.)