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A114889 a(1)=1 and, for n>1, a(n) is the smallest integer greater than a(n-1) such that a(n)+a(i) is not a power of 3, for i=1,..., n-1.

%I A114889 #4 Mar 30 2012 17:37:53
%S A114889 1,3,4,7,9,10,11,12,13,19,21,22,25,27,28,29,30,31,32,33,34,35,36,37,
%T A114889 38,39,40,55,57,58,61,63,64,65,66,67,73,75,76,79,81,82,83,84,85,86,87,
%U A114889 88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108
%N A114889 a(1)=1 and, for n>1, a(n) is the smallest integer greater than a(n-1) such that a(n)+a(i) is not a power of 3, for i=1,..., n-1.
%C A114889 The differences of {a(n)}, together with a conjectured formula for them, is given in A114890.
%e A114889 Given that a(1)=1, a(2)=3 and a(3)=4, we find that a(4)>5 since 5+4=9 and a(4)>6 since 6+3=9. But none of 7+1, 7+3, or 7+4 is a power of 3, so a(4)=7.
%Y A114889 Cf. A005652, A114890.
%K A114889 nonn
%O A114889 1,2
%A A114889 _John W. Layman_, Jan 04 2006