%I A117405
%S A117405 4,4,4,9,14,33,65,129,254,511,1027,2047,4097,8193,16382,32765,65531,
%T A117405 131073,262142,524289,1048577
%N A117405 Semiprime nearest to 2^n. (In case of a tie, choose the smaller).
%C A117405 Semiprime analogue of A117387 Prime nearest to 2^n. (In case of a tie, 
               choose the smaller). After n=2, never again is a(n) a power of 2.
%F A117405 a(n) = 2^n + A117406(n).
%e A117405 a(0) = 4 because 2^0 + 3 = 4 = A001358(1) and no semiprime is closer 
               to 2^0.
%e A117405 a(1) = 4 because 2^1 + 2 = 4 = A001358(1) and no semiprime is closer 
               to 2^1.
%e A117405 a(2) = 4 because 2^2 + 0 = 4 = A001358(1) and no semiprime is closer 
               to 2^2.
%e A117405 a(3) = 9 because 2^3 + 1 = 9 = 3^2 = A001358(3), no semiprime is closer 
               to 2^3.
%e A117405 a(4) = 14 because 2^4 - 2 = 14 = 2 * 7 = A001358(5), no semiprime is 
               closer.
%e A117405 a(5) = 33 because 2^5 + 1 = 33 = 3 * 11 and no semiprime is closer to 
               2^5.
%e A117405 a(6) = 65 because 2^6 + 1 = 65 = 5 * 13 and no semiprime is closer to 
               2^6.
%e A117405 a(7) = 129 because 2^7 + 1 = 129 = 3 * 43 and no semiprime is closer 
               to 2^7.
%e A117405 a(8) = 254 because 2^8 - 2 = 254 = 2 * 127 and no semiprime is closer 
               to 2^8.
%Y A117405 Cf. A000079, A001358, A117387, A117406.
%Y A117405 Sequence in context: A065734 A048761 A075561 this_sequence A013601 A035618 
               A151906
%Y A117405 Adjacent sequences: A117402 A117403 A117404 this_sequence A117406 A117407 
               A117408
%K A117405 easy,nonn,less
%O A117405 0,1
%A A117405 Jonathan Vos Post (jvospost3(AT)gmail.com), Mar 13 2006