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 A130249 Maximal index k of a Jacobsthal number such that A001045(k)<=n (the 'lower' Jacobsthal inverse). 13
 0, 2, 2, 3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 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, 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Inverse of the Jacobsthal sequence (A001045), nearly, since a(A001045(n))=n except for n=1 (see A130250 for another version). a(n)+1 is equal to the partial sum of the Jacobsthal indicator sequence (see A105348). LINKS G. C. Greubel, Table of n, a(n) for n = 0..10000 FORMULA a(n) = floor(log_2(3n+1)). a(n) = A130250(n+1) - 1 = A130253(n) - 1. G.f.: 1/(1-x)*(Sum_{k>=1} x^A001045(k)). EXAMPLE a(12)=5, since A001045(5)=11<=12, but A001045(6)=21>12. MATHEMATICA Table[Floor[Log[2, 3*n + 1]], {n, 0, 50}] (* G. C. Greubel, Jan 08 2018 *) PROG (PARI) for(n=0, 30, print1(floor(log(3*n+1)/log(2)), ", ")) \\ G. C. Greubel, Jan 08 2018 (MAGMA) [Floor(Log(3*n+1)/Log(2)): n in [0..30]]; // G. C. Greubel, Jan 08 2018 CROSSREFS For partial sums see A130251. Other related sequences A130250, A130253, A105348. A001045, A130233, A130241. Sequence in context: A143489 A274102 A261100 * A286105 A061071 A122258 Adjacent sequences:  A130246 A130247 A130248 * A130250 A130251 A130252 KEYWORD nonn AUTHOR Hieronymus Fischer, May 20 2007 STATUS approved

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Last modified October 14 15:14 EDT 2019. Contains 328019 sequences. (Running on oeis4.)