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 A138278 #21 Jan 14 2024 02:27:46
%S A138278 1,2,4,8,16,24,40,80,120,200,400,600,1000,2000,3000,5000,10000,15000,
%T A138278 25000,50000,75000,125000,250000,375000,625000,1250000,1875000,
%U A138278 3125000,6250000,9375000,15625000,31250000,46875000,78125000,156250000,234375000,390625000
%N A138278 Sequence identical to its third differences in absolute values.
%H A138278 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,5).
%F A138278 From _R. J. Mathar_, Mar 23 2010: (Start)
%F A138278 a(n) = 5*a(n-3), n>5.
%F A138278 G.f.: (3*x^3+6*x^4+4*x^5+1+2*x+4*x^2)/(1-5*x^3). (End)
%F A138278 Sum_{n>=0} 1/a(n) = 391/192. - _Amiram Eldar_, Jan 14 2024
%t A138278 Join[{1,2,4},LinearRecurrence[{0,0,5},{8,16,24},40]] (* _Harvey P. Dale_, Dec 08 2011 *)
%Y A138278 Cf. A131292, A131665, A132158, A132418, A132658.
%K A138278 nonn,easy
%O A138278 0,2
%A A138278 _Paul Curtz_, May 06 2008
%E A138278 Edited by _Charles R Greathouse IV_, Mar 18 2010
%E A138278 More terms from _Harvey P. Dale_, Dec 08 2011