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A130250 Minimal index k of a Jacobsthal number such that A001045(k)>=n (the 'upper' Jacobsthal inverse). 7
0, 1, 3, 3, 4, 4, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

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).

LINKS

Table of n, a(n) for n=0..100.

FORMULA

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)}.

EXAMPLE

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

CROSSREFS

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

Sequence in context: A021303 A240622 * A130253 A145288 A075324 A134993

Adjacent sequences:  A130247 A130248 A130249 * A130251 A130252 A130253

KEYWORD

nonn

AUTHOR

Hieronymus Fischer, May 20 2007

STATUS

approved

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Last modified April 24 04:19 EDT 2018. Contains 302984 sequences. (Running on oeis4.)