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 A087777 a(1) = ... = a(4) = 1; a(n) = a(n - a(n-2)) + a(n - a(n-4)). 6
 1, 1, 1, 1, 2, 4, 6, 7, 7, 5, 3, 8, 9, 11, 12, 9, 9, 13, 11, 9, 13, 16, 13, 19, 16, 11, 14, 16, 21, 22, 14, 14, 19, 17, 22, 27, 25, 16, 20, 28, 22, 22, 26, 25, 24, 32, 26, 22, 29, 29, 32, 35, 32, 27, 26, 34, 30, 33, 40, 25, 27, 46, 40, 33, 32, 28, 36, 50, 44, 31, 36, 38, 46, 53, 41, 29, 41 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS This is the sequence Q(2,4) in the Hofstadter-Huber classification. It is not known if this sequence is defined for all positive n. Balamohan et al. comment that it shows "inscrutably wild behavior". LINKS N. J. A. Sloane, Table of n, a(n) for n = 1..10000 B. Balamohan, A. Kuznetsov and S. Tanny, On the behavior of a variant of Hofstadter's Q-sequence, J. Integer Sequences, Vol. 10 (2007), #07.7.1. Nathan Fox, A Slow Relative of Hofstadter's Q-Sequence, arXiv:1611.08244 [math.NT], 2016. D. R. Hofstadter, Curious patterns and non-patterns in a family of meta-Fibonacci recursions, Lecture in Doron Zeilberger's Experimental Mathematics Seminar, Rutgers University, April 10 2014; Part 1, Part 2. D. R. Hofstadter, Plot of first 100000 terms MAPLE a := proc(n) option remember; if n<=4 then 1 else if n > a(n-2) and n > a(n-4) then RETURN(a(n-a(n-2))+a(n-a(n-4))); else ERROR(" died at n= ", n); fi; fi; end; MATHEMATICA a[n_] := a[n] = If[n <= 4, 1, a[n - a[n - 2]] + a[n - a[n - 4]]]; Array[a, 80] (* Jean-François Alcover, Nov 24 2017 *) PROG (MAGMA) [n le 4 select 1 else Self(n-Self(n-2))+Self(n-Self(n-4)): n in [1..80]]; // Vincenzo Librandi, Sep 10 2016 CROSSREFS Cf. A005185 (Q(1,2)), A063882 (Q(1,4)), A046700. Sequence in context: A114431 A167689 A058184 * A030118 A331379 A023835 Adjacent sequences:  A087774 A087775 A087776 * A087778 A087779 A087780 KEYWORD nonn AUTHOR Roger L. Bagula, Oct 05 2003 EXTENSIONS Edited by N. J. A. Sloane, Nov 06 2007 STATUS approved

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Last modified June 23 11:59 EDT 2021. Contains 345398 sequences. (Running on oeis4.)