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A107736 Pentagonal numbers that are half other pentagonal numbers. 3
35, 46651605, 62126595542551, 82734857056306152425, 110179167429819564875005515, 146727139774551997160896788291901, 195398586217617559179696685958485684415, 260215032846061623065656040447357907946787025, 346532002251364709713039450689133092337489050568051 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Colin Barker, Table of n, a(n) for n = 1..163

Index entries for linear recurrences with constant coefficients, signature (1331715,-1331715,1).

FORMULA

a(n) = ((A001653(4n-2)^2-1)/24.

G.f.: -x*(x^2+41580*x+35) / ((x-1)*(x^2-1331714*x+1)). - Colin Barker, Jun 18 2015

EXAMPLE

a(2)=((A001653(6)^2-1)/24=(33461^2-1)/24=46651605.

PROG

(PARI) Vec(-x*(x^2+41580*x+35)/((x-1)*(x^2-1331714*x+1)) + O(x^20)) \\ Colin Barker, Jun 18 2015

CROSSREFS

Cf. A001653, A000326.

Sequence in context: A110596 A286178 A126029 * A261121 A139474 A240129

Adjacent sequences:  A107733 A107734 A107735 * A107737 A107738 A107739

KEYWORD

nonn,easy

AUTHOR

Franz Vrabec, Aug 26 2006

STATUS

approved

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Last modified January 18 07:18 EST 2019. Contains 319269 sequences. (Running on oeis4.)