Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #18 Nov 11 2023 10:59:53
%S -80,-79,-77,-73,-65,-49,-17,47,175,431,943,1967,4015,8111,16303,
%T 32687,65455,130991,262063,524207,1048495,2097071,4194223,8388527,
%U 16777135,33554351,67108783,134217647,268435375,536870831,1073741743,2147483567,4294967215
%N a(n) = 2^n - 81.
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2).
%F From _Chai Wah Wu_, Jan 17 2020: (Start)
%F a(n) = 3*a(n-1) - 2*a(n-2) for n > 1.
%F G.f.: (161*x - 80)/((x - 1)*(2*x - 1)). (End)
%F From _Elmo R. Oliveira_, Nov 11 2023: (Start)
%F a(n) = 2*a(n-1) + 81 with a(0) = -80.
%F E.g.f.: exp(2*x) - 81*exp(x). (End)
%t Table[2^n - 81, {n, 0, 40}] (* _T. D. Noe_, Dec 04 2012 *)
%Y Cf. A000225, A036563, A185346, A220087.
%K sign,easy
%O 0,1
%A _Andreas Rieber_, Dec 04 2012