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A158186 a(n) = 10*n^2 - 7*n + 1. 3

%I

%S 1,4,27,70,133,216,319,442,585,748,931,1134,1357,1600,1863,2146,2449,

%T 2772,3115,3478,3861,4264,4687,5130,5593,6076,6579,7102,7645,8208,

%U 8791,9394,10017,10660,11323,12006,12709,13432,14175,14938,15721,16524,17347

%N a(n) = 10*n^2 - 7*n + 1.

%C Sequence found by reading the segment (1, 4) together with the line (one of the diagonal axes) from 4, in the direction 4, 27, ..., in the square spiral whose vertices are the generalized heptagonal numbers A085787. - _Omar E. Pol_, Sep 10 2011

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

%F a(n) = (2*n-1)*(5*n-1).

%F a(n) = A033571(n) - A008596(n) = A010010(n) - A033571(n).

%F G.f.: (1+x+18*x^2)/(1-x)^3. - _Jaume Oliver Lafont_, Mar 27 2009

%F a(n) = a(n-1) + 20*n - 17 (with a(0)=1). - _Vincenzo Librandi_, Dec 03 2010

%o (PARI) a(n)=10*n^2-7*n+1 \\ _Charles R Greathouse IV_, Jun 17 2017

%K nonn,easy

%O 0,2

%A _Reinhard Zumkeller_, Mar 13 2009

%E Typo in definition corrected by _Reinhard Zumkeller_, Dec 03 2009

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Last modified July 17 16:58 EDT 2019. Contains 325107 sequences. (Running on oeis4.)