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A136017 a(n) = 36n^2 - 1. 11
35, 143, 323, 575, 899, 1295, 1763, 2303, 2915, 3599, 4355, 5183, 6083, 7055, 8099, 9215, 10403, 11663, 12995, 14399, 15875, 17423, 19043, 20735, 22499, 24335, 26243, 28223, 30275, 32399, 34595, 36863, 39203, 41615, 44099, 46655, 49283, 51983 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Sum_{k>=1} (-1)^(k+1)/a(k) = (Pi-3)/6. - Jaume Oliver Lafont, Oct 20 2009

Product_{n >= 1} A016910(n) / a(n) = Pi / 3. - Fred Daniel Kline, Jun 09 2016

The least common multiple of 6*n+1 and 6*n-1. - Colin Barker, Feb 11 2017

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

X. Gourdon and P. Sebah, Collection of series for Pi

Edward Everett Withford, Pell Equation

Wolfram MathWorld, Pell Equation

Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

FORMULA

O.g.f.: x*(-35-38*x+x^2)/(-1+x)^3 = 1-35/(-1+x)-108/(-1+x)^2-72/(-1+x)^3 . - R. J. Mathar, Dec 12 2007

a(n) = A061037(12n+10)=(6n-1)*(6n+1)=36*n^2-1. From Balmer spectrum of hydrogen. - Paul Curtz, Sep 25 2008

E.g.f.: 1 + (36 x^2 + 26 x - 1) exp(x). - Robert Israel, Jun 09 2016

MATHEMATICA

Table[36n^2 - 1, {n, 1, 100}]

PROG

(PARI) a(n)=36*n^2-1 \\ Jaume Oliver Lafont, Oct 20 2009

(MAGMA)[36*n^2 - 1: n in [1..50]]; // Vincenzo Librandi, Jul 09 2012

CROSSREFS

Cf. A088878, A023208, A136016, A061037, A016910.

Sequence in context: A220014 A157286 A290560 * A048628 A048629 A133534

Adjacent sequences:  A136014 A136015 A136016 * A136018 A136019 A136020

KEYWORD

nonn,easy

AUTHOR

Artur Jasinski, Dec 10 2007

STATUS

approved

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Last modified December 17 09:23 EST 2018. Contains 318193 sequences. (Running on oeis4.)