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 A084181 #10 Jan 02 2019 12:45:27
%S A084181 1,1,7,1,31,1,127,1,511,1,2047,1,8191,1,32767,1,131071,1,524287,1,
%T A084181 2097151,1,8388607,1,33554431,1,134217727,1,536870911,1,2147483647,1,
%U A084181 8589934591,1,34359738367,1,137438953471,1,549755813887,1,2199023255551
%N A084181 2^n+(-2)^n-(-1)^n.
%C A084181 Binomial transform is A084182.
%H A084181 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-1,4,4).
%F A084181 a(n)=2^n+(-2)^n-(-1)^n;
%F A084181 G.f.: (1+2x+4x^2)/((1+x)(1+2x)(1-2x));
%F A084181 E.g.f.: exp(2x)-exp(-x)+exp(-2x).
%t A084181 LinearRecurrence[{-1,4,4},{1,1,7},50] (* or *) Riffle[ LinearRecurrence[ {5,-4},{1,7},30],1] (* _Harvey P. Dale_, Jan 02 2019 *)
%Y A084181 Cf. A083420.
%K A084181 easy,nonn
%O A084181 0,3
%A A084181 _Paul Barry_, May 19 2003