Tetrahedral sphere packing

[N. J. A. Sloane]

Seqfans, 
     What is the following "minimal shifting logs" sequence? 
 
Increasing sequence of least terms, starting with a(1)=1, that satisfy: 
exp(Sum_{n>=1} a(n+m)*x^n/n) is an integer sequence for all m>=0. 
 
Example. 
Sequence B defined by b(n) = 2^n - 1 for n>=1 
satisfies the condition since the following g.f.s 
form integer sequences: 
exp(x + 3x^2/2 + 7x^3/3 + 15x^4/4 + 31x^5/5 +...);
exp(3x + 7x^2/2 + 15x^3/3 + 31x^4/4 + 63x^5/5 +...);
exp(7x + 15x^2/2 + 31x^3/3 + 63x^4/4 + 127x^5/5 +...);
exp(15x + 31x^2/2 + 63x^3/3 + 127x^4/4 +...); 
etc. 
The coefficients in these logarithmic series are successive shiftings of
B 
in such a way that the exponential always results in an integer series. 
 
Question: does this sequence B=[1,3,7,15,31,63,...] form the 
minimal increasing sequence that satisfies the condition? 
Or is there a different sequence that forms the minimal shifting logs? 
 
      Paul