This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A158186 #31 Sep 22 2022 01:57:06
%S A158186 1,4,27,70,133,216,319,442,585,748,931,1134,1357,1600,1863,2146,2449,
%T A158186 2772,3115,3478,3861,4264,4687,5130,5593,6076,6579,7102,7645,8208,
%U A158186 8791,9394,10017,10660,11323,12006,12709,13432,14175,14938,15721,16524,17347
%N A158186 a(n) = 10*n^2 - 7*n + 1.
%C A158186 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 A158186 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A158186 a(n) = (2*n-1)*(5*n-1).
%F A158186 a(n) = A033571(n) - A008596(n) = A010010(n) - A033571(n).
%F A158186 G.f.: (1+x+18*x^2)/(1-x)^3. - _Jaume Oliver Lafont_, Mar 27 2009
%F A158186 a(n) = a(n-1) + 20*n - 17 (with a(0)=1). - _Vincenzo Librandi_, Dec 03 2010
%F A158186 Sum_{n>=0} 1/a(n) = 1 + (2*sqrt(1+2/sqrt(5))*Pi - 2*sqrt(5)*log(phi) - 5*log(5) + 8*log(2))/12, where phi is the golden ratio (A001622). - _Amiram Eldar_, Sep 22 2022
%t A158186 Table[10n^2-7n+1,{n,0,50}] (* or *) LinearRecurrence[{3,-3,1},{1,4,27},50] (* _Harvey P. Dale_, Apr 06 2020 *)
%o A158186 (PARI) a(n)=10*n^2-7*n+1 \\ _Charles R Greathouse IV_, Jun 17 2017
%Y A158186 Cf. A001622, A008596, A010010, A033571, A085787.
%K A158186 nonn,easy
%O A158186 0,2
%A A158186 _Reinhard Zumkeller_, Mar 13 2009
%E A158186 Typo in definition corrected by _Reinhard Zumkeller_, Dec 03 2009