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Define k by A280864(k) = 2^n; then a(n) = A280864(k-1)/2, or -1 if that is not an integer.
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%I #5 Feb 10 2017 14:09:13

%S 1,3,7,19,41,74,131,302,523,1031,2458,4132,8209,16381,32832,84614,

%T 131101,262139

%N Define k by A280864(k) = 2^n; then a(n) = A280864(k-1)/2, or -1 if that is not an integer.

%C It is known that every even number appears in A280864, and that the powers of 2 appear in increasing order.

%C If it were known that A280864(k-1) were always even, this would prove that A280864 contains every odd number, and so complete the proof that A280864 contains every positive number.

%Y Cf. A280864, A280746.

%K nonn,more

%O 2,2

%A _N. J. A. Sloane_, Feb 10 2017