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Powers of 3 which are not powers of 3^3.
0

%I #9 Jul 31 2015 11:23:01

%S 3,9,81,243,2187,6561,59049,177147,1594323,4782969,43046721,129140163,

%T 1162261467,3486784401,31381059609,94143178827,847288609443,

%U 2541865828329,22876792454961,68630377364883,617673396283947

%N Powers of 3 which are not powers of 3^3.

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0, 27).

%F a(n) = a(n-1)*a(n-2)/a(n-3) = 27*a(n-2) = 3^A001651(n).

%F a(2n) = 3^(3n+1), a(2n+1) = 3^(3n+2).

%t With[{nn=40},Complement[3^Range[nn],27^Range[Floor[nn/3]]]] (* or *) LinearRecurrence[{0,27},{3,9},40] (* _Harvey P. Dale_, Jul 17 2012 *)

%Y Cf. A013732 and A013733. Consists of numbers in A000244 which are not in A009971. See A004171 for powers of 2 which are not powers of 2^2.

%K nonn,easy

%O 0,1

%A _Henry Bottomley_, Jun 20 2000