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A206399 a(0) = 1; for n>0, a(n) = 41*n^2 + 2. 35

%I

%S 1,43,166,371,658,1027,1478,2011,2626,3323,4102,4963,5906,6931,8038,

%T 9227,10498,11851,13286,14803,16402,18083,19846,21691,23618,25627,

%U 27718,29891,32146,34483,36902,39403,41986,44651,47398,50227,53138,56131,59206,62363

%N a(0) = 1; for n>0, a(n) = 41*n^2 + 2.

%C Apart from the first term, numbers of the form (r^2+2*s^2)*n^2+2 = (r*n)^2+(s*n-1)^2+(s*n+1)^2: in this case is r=3, s=4. After 1, all terms are in A000408.

%H Bruno Berselli, <a href="/A206399/b206399.txt">Table of n, a(n) for n = 0..1000</a>

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

%F O.g.f.: (1 + x)*(1 + 39*x + x^2)/(1 - x)^3.

%t Join[{1}, 41 Range[39]^2 + 2]

%t CoefficientList[Series[(1 + x) (1 + 39 x + x^2) / (1 - x)^3, {x, 0, 40}], x] (* _Vincenzo Librandi_, Aug 18 2013 *)

%o (MAGMA) [n eq 0 select 1 else 41*n^2+2: n in [0..39]];

%o (MAGMA) I:=[1,43,166,371]; [n le 4 select I[n] else 3*Self(n-1)-3*Self(n-2)+Self(n-3): n in [1..41]]; // _Vincenzo Librandi_, Aug 18 2013

%o (PARI) a(n)=if(n,41*n^2+2,1) \\ _Charles R Greathouse IV_, Sep 24 2015

%Y Sequences of the same type: A005893, A005897, A005899, A005901, A005903, A005905, A005914, A005918, A005919, A008527, A010000-A010023.

%K nonn,easy

%O 0,2

%A _Bruno Berselli_, Feb 07 2012

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Last modified August 21 22:52 EDT 2018. Contains 313958 sequences. (Running on oeis4.)