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 A081219 #22 Aug 02 2025 12:16:52
%S A081219 1,34,259,1092,3333,8294,17927,34952,62985,106666,171787,265420,
%T A081219 396045,573678,809999,1118480,1514513,2015538,2641171,3413332,4356373,
%U A081219 5497206,6865431,8493464,10416665,12673466,15305499,18357724,21878557,25919998
%N A081219 One sixtieth the product of primitive Pythagorean triangles' sides whose odd values differ by 2.
%C A081219 If Y and Z are 2-blocks of a (2n+1)-set X then a(n-2) is the number of 7-subsets of X intersecting both Y and Z. - _Milan Janjic_, Oct 28 2007
%H A081219 Milan Janjic, <a href="https://old.pmf.unibl.org/wp-content/uploads/2017/10/enumfor.pdf">Two Enumerative Functions</a>
%H A081219 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (6,-15,20,-15,6,-1).
%F A081219 a(n) = n*(16*n^4 - 1)/15.
%F A081219 G.f.: x*(x^4+28*x^3+70*x^2+28*x+1) / (x-1)^6. - _Colin Barker_, Oct 06 2014
%F A081219 E.g.f.: exp(x)*x*(15 + 240*x + 400*x^2 + 160*x^3 + 16*x^4)/15. - _Stefano Spezia_, Aug 02 2025
%t A081219 LinearRecurrence[{6,-15,20,-15,6,-1},{1,34,259,1092,3333,8294},30] (* _Harvey P. Dale_, Feb 11 2024 *)
%o A081219 (PARI) Vec(x*(x^4+28*x^3+70*x^2+28*x+1)/(x-1)^6 + O(x^100)) \\ _Colin Barker_, Oct 06 2014
%Y A081219 Cf. A081752.
%K A081219 easy,nonn
%O A081219 1,2
%A A081219 _Lekraj Beedassy_, Apr 18 2003
%E A081219 More terms from _Ray Chandler_, Oct 28 2003