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%I #2 Mar 30 2012 18:41:20
%S 1,4,12,32,76,176,384,832,1740,3632,7440,15232,30848,62464,125760,
%T 253184,508108,1019696,2043024,4093312,8194064,16403008,32821248,
%U 65672960,131376768,262815232,525692928,1051510784,2103147328
%N a(0)=1, a(2n) = 2a(2n-1)+a(n), a(2n+1) = 2a(2n)+2a(n).
%C a(n) ~ 2^(n+e) with e = 2.9701632052178...
%F G.f. prod(k>=0, (1+2x^2^k)/(1-2x^2^k)).
%o (PARI) a(n)=if(n<1,n<1,if(n%2==0,2*a(n-1)+a(n/2),2*a(n-1)+2*a((n-1)/2)))
%Y Cf. A018819.
%K nonn,easy
%O 0,2
%A _Ralf Stephan_, Jun 28 2003
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