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A189833 a(n) = n^2 + 8. 7

%I #39 Feb 05 2024 02:27:29

%S 8,9,12,17,24,33,44,57,72,89,108,129,152,177,204,233,264,297,332,369,

%T 408,449,492,537,584,633,684,737,792,849,908,969,1032,1097,1164,1233,

%U 1304,1377,1452,1529,1608,1689,1772,1857,1944,2033

%N a(n) = n^2 + 8.

%C From _César Eliud Lozada_, Mar 29 2021: (Start)

%C Numbers a(n) such that sqrt( a(n) + 4*n*sqrt(2) ) = n + 2*sqrt(2). Examples:

%C For n=1: sqrt( 9 + 4*sqrt(2)) = 1 + 2*sqrt(2),

%C For n=2: sqrt(12 + 8*sqrt(2)) = 2 + 2*sqrt(2),

%C For n=3: sqrt(17 + 12*sqrt(2)) = 3 + 2*sqrt(2). (End)

%H G. C. Greubel, <a href="/A189833/b189833.txt">Table of n, a(n) for n = 0..10000</a> (terms 0..955 from Vincenzo Librandi)

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).

%F From _G. C. Greubel_, Jan 13 2018: (Start)

%F G.f.: (8 - 15*x + 9*x^2)/(1 - x)^3.

%F E.g.f.: (8 + x + x^2)*exp(x). (End)

%F From _Amiram Eldar_, Jul 04 2020: (Start)

%F Sum_{n>=0} 1/a(n) = (1 + 2*sqrt(2)*Pi*coth(2*sqrt(2)*Pi))/16.

%F Sum_{n>=0} (-1)^n/a(n) = (1 + 2*sqrt(2)*Pi*cosech(2*sqrt(2)*Pi))/16. (End)

%F From _Amiram Eldar_, Feb 05 2024: (Start)

%F Product_{n>=0} (1 - 1/a(n)) = (sqrt(7/2)/2)*sinh(sqrt(7)*Pi)/sinh(2*sqrt(2)*Pi).

%F Product_{n>=0} (1 + 1/a(n)) = (3/(2*sqrt(2)))*sinh(3*Pi)/sinh(2*sqrt(2)*Pi). (End)

%t Table[n^2+8,{n,0,100}]

%t LinearRecurrence[{3,-3,1},{8,9,12},50] (* _Harvey P. Dale_, Jun 21 2022 *)

%o (Magma) [n^2+8: n in [0..50]]; // _Vincenzo Librandi_, Apr 29 2011

%o (PARI) a(n)=n^2+8 \\ _Charles R Greathouse IV_, Jun 17 2017

%Y Cf. A002522, A059100, A117950, A087475.

%K nonn,easy

%O 0,1

%A _Vladimir Joseph Stephan Orlovsky_, Apr 28 2011

%E Offset changed from 1 to 0 by _Vincenzo Librandi_, Apr 29 2011

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Last modified March 29 05:48 EDT 2024. Contains 371265 sequences. (Running on oeis4.)