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 A137879 #20 Jun 07 2021 04:40:48
%S A137879 1,133,615,64107,296429,30899441,142878163,14893466455,68866978137,
%T A137879 7178619931869,33193740583871,3460079913694403,15999314094447685,
%U A137879 1667751339780770377,7711636199783200299,803852685694417627311,3716992648981408096433
%N A137879 Numbers k such that k^2 is a 17-gonal number.
%C A137879 Corresponding 17-gonal numbers equal k^2 are listed in A137878.
%C A137879 The 17-gonal numbers A051869(n) = n*(15n - 13)/2 are perfect squares for indices n listed in A137880. Note that all such indices are also perfect squares of numbers listed in A137881.
%H A137879 Harvey P. Dale, <a href="/A137879/b137879.txt">Table of n, a(n) for n = 1..745</a>
%H A137879 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,482,0,-1).
%F A137879 a(n) = sqrt(A137878(n)) = sqrt(A051869(A137880(n))) = sqrt(A051869(A137881(n)^2)).
%F A137879 From _Max Alekseyev_, Oct 19 2008: (Start)
%F A137879 For n>=5, a(n) = 482*a(n-2) - a(n-4).
%F A137879 a(2n) = (-60 + 17*sqrt(30))/120 * (11 + 2*sqrt(30))^(2n) + (-60 - 17*sqrt(30))/120 * (11 - 2*sqrt(30))^(2n).
%F A137879 a(2n+1) = (60 + 17*sqrt(30))/120 * (11 + 2*sqrt(30))^(2n) + (60 - 17*sqrt(30))/120 * (11 - 2*sqrt(30))^(2n). (End)
%t A137879 LinearRecurrence[{0,482,0,-1},{1,133,615,64107},20] (* _Harvey P. Dale_, May 12 2014 *)
%o A137879 (PARI) is(n)=ispolygonal(n^2,17) \\ _Charles R Greathouse IV_, Oct 16 2015
%Y A137879 Cf. A051869 (17-gonal numbers), A137878 (17-gonal numbers that are perfect squares), A137880, A137881.
%K A137879 nonn,easy
%O A137879 1,2
%A A137879 _Alexander Adamchuk_, Feb 19 2008
%E A137879 Extended by _Max Alekseyev_, Oct 19 2008