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 A345702 #13 Jun 24 2021 19:21:29
%S A345702 -1,647,41471,472391,2654207,10124999,30233087,76236551,169869311,
%T A345702 344373767,647999999,1147971527,1934917631,3127772231,4879139327,
%U A345702 7381124999,10871635967,15641144711,22039921151,30485730887,41471999999,55576446407,73470177791,95927256071,123834728447
%N A345702 Numbers that can be written as 2*a^2 - 1 and 3*b^3 - 1.
%H A345702 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (7,-21,35,-35,21,-7,1).
%F A345702 G.f.: x*(647*x^6+36942*x^5+195681*x^4+195716*x^3+36921*x^2+654*x-1)/(1-x)^7. - _Alois P. Heinz_, Jun 24 2021
%F A345702 a(n) = 648*(n-1)^6 - 1 = 648*A001014(n-1) - 1. - _Hugo Pfoertner_, Jun 24 2021
%e A345702 647 = 2*18^2 - 1 = 3*6^3 - 1. Thus, 647 is in this sequence.
%t A345702 Intersection[Table[2 n^2 - 1, {n, 300000}], Table[3 n^3 - 1, {n, 100000}]]
%Y A345702 Intersection of A056220 and A345701.
%K A345702 sign,easy
%O A345702 1,2
%A A345702 _Tanya Khovanova_, Jun 24 2021