0,3

Inverse of the Jacobsthal sequence (A001045), nearly, since a(A001045(n))=n except for n=2 (see A130249 for another version). a(n+1) is equal to the partial sum of the Jacobsthal indicator sequence (see A105348).

a(n)=ceiling(log_2(3n-1))=1+floor(log_2(3n-2)) for n>=1. Also true: a(n)=A130249(n-1)+1=A130253(n-1) for n>=1. G.f.: g(x)=x/(1-x)*sum{k>=0, x^A001045(k)}.

a(10)=5 because A001045(5)=11>=10, but A001045(4)=5<10

For partial sums see A130252. Other related sequences A130249, A130253, A105348. A001045, A130234, A130242.

Sequence in context: A136546 A058729 A021303 this_sequence A130253 A075324 A134993

Adjacent sequences: A130247 A130248 A130249 this_sequence A130251 A130252 A130253

nonn

Hieronymus Fischer (Hieronymus.Fischer(AT)gmx.de), May 20 2007