A087777 -id:A087777 - cp's OEIS frontend

A063882 a(n) = a(n - a(n - 1)) + a(n - a(n - 4)), with a(1) = ... = a(4) = 1.

1, 1, 1, 1, 2, 3, 4, 5, 5, 6, 6, 7, 8, 8, 9, 9, 10, 11, 11, 11, 12, 12, 13, 14, 14, 15, 15, 16, 17, 17, 17, 18, 18, 19, 20, 20, 21, 21, 22, 22, 22, 23, 23, 24, 25, 25, 26, 26, 27, 27, 28, 29, 29, 29, 30, 30, 31, 32, 32, 33, 33, 34, 34, 34, 35, 35, 36, 37, 37, 38, 38, 39, 39, 40

Offset: 1

Theodor Schlickmann (Theodor.Schlickmann(AT)cec.eu.int), Aug 28 2001

A captivating recursive function. A meta-Fibonacci recursion.
This has been completely analyzed by Balamohan et al. They prove that the sequence a(n) is monotonic, with successive terms increasing by 0 or 1, so the sequence hits every positive integer.
They demonstrate certain special structural properties and periodicities of the associated frequency sequence (the number of times a(n) hits each positive integer) that make possible an iterative computation of a(n) for any value of n.
Further, they derive a natural partition of the a-sequence into blocks of consecutive terms ("generations") with the property that terms in one block determine the terms in the next.
a(A202014(n)) = n and a(m) < n for m < A202014(n). [Reinhard Zumkeller, Dec 08 2011]

T. D. Noe and N. J. A. Sloane, Table of n, a(n) for n = 1..10000
Altug Alkan, On a Generalization of Hofstadter's Q-Sequence: A Family of Chaotic Generational Structures, Complexity (2018) Article ID 8517125.
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.
Jonathan H. B. Deane and Guido Gentile, A diluted version of the problem of the existence of the Hofstadter sequence, arXiv:2311.13854 [math.NT], 2023.
A. Isgur, R. Lech, S. Moore, S. Tanny, Y. Verberne, and Y. Zhang, Constructing New Families of Nested Recursions with Slow Solutions, SIAM J. Discrete Math., 30(2), 2016, 1128-1147. (20 pages); DOI:10.1137/15M1040505
Kellie O'Connor Gutman, V(n) = V(n - V(n - 1)) + V(n - V(n - 4)), The Mathematical Intelligencer, Volume 23, Number 3, Summer 2001, page 50.
Index entries for Hofstadter-type sequences

Cf. A132157. For partial sums see A129632.
A136036(n) = a(n+1) - a(n).
Cf. A063892, A087777.
Cf. A132174, A132175, A132176, A132177.
Cf. A202016 (occur only once).

a063882 n = a063882_list !! (n-1)
a063882_list = 1 : 1 : 1 : 1 : zipWith (+)
   (map a063882 $ zipWith (-) [5..] a063882_list)
   (map a063882 $ zipWith (-) [5..] $ drop 3 a063882_list)
-- Reinhard Zumkeller, Dec 08 2011

a := proc(n) option remember; if n<=4 then 1 else if n > a(n-1) and n > a(n-4) then RETURN(a(n-a(n-1))+a(n-a(n-4))); else ERROR(" died at n= ", n); fi; fi; end;

a[1]=a[2]=a[3]=a[4]=1;a[n_]:=a[n]=a[n-a[n-1]]+a[n-a[n-4]];Table[a[n],{n,80}]

n/2 < a(n) <= n/2 + log_2 (n) - 1 for all n > 6 [Balamohan et al., Proposition 5].

Edited by N. J. A. Sloane, Nov 06 2007

Mathematica program corrected by Harvey P. Dale, Jan 24 2025

A240811 a(n) = length (or lifetime) of the meta-Fibonacci sequence f(1) = ... = f(n) = 1; f(k)=f(k-f(k-2))+f(k-f(k-n)) if that sequence is only defined for finitely many terms, or 0 if that sequence is infinite.

Original entry on oeis.org

14, 54, 0, 37, 30, 63, 368, 47, 46, 108, 188, 118, 62, 209, 126, 197, 78, 127, 190, 141, 94, 130, 138, 226, 110, 134, 158, 138, 126, 170, 242, 371, 142, 190, 178, 225, 158, 206, 214, 304, 174, 226, 238, 245, 190, 250, 262, 328, 206, 234, 278, 357, 222, 290

Offset: 2

N. J. A. Sloane, Apr 15 2014

nonn

The term a(4) = 0 is only conjectural.

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.

Lars Blomberg, Table of n, a(n) for n = 2..10000, "infinity" = 10^8.
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, Graph of first 100 terms
Index entries for Hofstadter-type sequences

Cf. A063892, A087777, A240817 (sequences for n=3..5).
See A240814 for another version.
A diagonal of the triangle in A240813.

More terms from Lars Blomberg, Oct 24 2014

A304490 a(1) = a(2) = a(3) = 1, a(4) = 5, a(5) = 6, a(6) = 4; a(n) = a(n-a(n-2)) + a(n-a(n-4)) for n > 6.

Original entry on oeis.org

1, 1, 1, 5, 6, 4, 5, 6, 6, 9, 10, 5, 6, 12, 12, 15, 16, 5, 6, 18, 18, 21, 22, 5, 6, 24, 24, 27, 28, 5, 6, 30, 30, 33, 34, 5, 6, 36, 36, 39, 40, 5, 6, 42, 42, 45, 46, 5, 6, 48, 48, 51, 52, 5, 6, 54, 54, 57, 58, 5, 6, 60, 60, 63, 64, 5, 6, 66, 66, 69, 70, 5, 6, 72, 72, 75, 76, 5, 6, 78, 78, 81, 82, 5, 6

Offset: 1

Altug Alkan, May 13 2018

A quasi-periodic solution to the recurrence a(n) = a(n-a(n-2)) + a(n-a(n-4)). Although A087777 and A240809 are highly chaotic, this sequence is completely predictable thanks to its initial conditions.

Index entries for linear recurrences with constant coefficients, signature (2, -3, 4, -5, 6, -5, 4, -3, 2, -1).

Cf. A087777, A240809, A244477, A296518, A296786.

q=vector(85); q[1]=1;q[2]=1;q[3]=1;q[4]=5;q[5]=6;q[6]=4; for(n=7, #q, q[n] = q[n-q[n-2]]+q[n-q[n-4]]); q

a(6*k) = 5, a(6*k+1) = 6, a(6*k+2) = a(6*k+3) = 6*k, a(6*k+4) = 6*k+3, a(6*k+5) = 6*k+4 for k > 1.
Conjectures from Colin Barker, May 14 2018: (Start)
G.f.: x*(1 - x + 2*x^2 + 2*x^3 + 2*x^5 - x^6 + 4*x^7 - 3*x^8 + x^9 - x^10 - 2*x^11 + 2*x^12 - x^13 + x^14 + x^15 - x^16) / ((1 - x)^2*(1 - x + x^2)^2*(1 + x + x^2)^2).
a(n) = 2*a(n-1) - 3*a(n-2) + 4*a(n-3) - 5*a(n-4) + 6*a(n-5) - 5*a(n-6) + 4*a(n-7) - 3*a(n-8) + 2*a(n-9) - a(n-10) for n>17.
(End)

A304590 a(1) = a(2) = a(3) = a(5) = 1, a(4) = 2, a(6) = 3; a(n) = a(n-a(n-3)) + a(n-a(n-6)) for n > 6.

Original entry on oeis.org

1, 1, 1, 2, 1, 3, 4, 8, 11, 11, 12, 12, 12, 4, 3, 3, 13, 6, 7, 7, 9, 10, 14, 9, 9, 19, 12, 13, 14, 15, 16, 18, 15, 15, 22, 18, 19, 10, 18, 18, 23, 18, 18, 24, 24, 26, 23, 24, 30, 31, 24, 29, 25, 30, 28, 25, 27, 29, 30, 30, 33, 37, 33, 38, 35, 33, 29, 31, 36, 41, 36, 36, 42, 28, 36, 37, 53, 36, 37, 41, 48, 48, 33

Offset: 1

Altug Alkan, May 15 2018

nonn

Altug Alkan, Table of n, a(n) for n = 1..10000

Cf. A005185, A063882, A087777, A240827.

a:=[1,1,1,2,1,3];; for n in [7..100] do a[n]:=a[n-a[n-3]]+a[n-a[n-6]]; od; a; # Muniru A Asiru, May 19 2018

f:= proc(n) option remember; procname(n-procname(n-3))+procname(n-procname(n-6)) end proc:
for i from 1 to 6 do f(i):= [1,1,1,2,1,3][i] od:
map(f, [$1..100]); # Robert Israel, May 16 2018

Nest[Append[#2, #2[[#1 - #2[[-3]] ]] + #2[[#1 - #2[[-6]] ]] ] & @@ {Length@ # + 1, #} &, {1, 1, 1, 2, 1, 3}, 77] (* Michael De Vlieger, Jul 20 2018 *)

q=vector(100); q[1]=q[2]=q[3]=q[5]=1;q[4]=2;q[6]=3; for(n=7, #q, q[n]=q[n-q[n-3]]+q[n-q[n-6]]); q

A304622 a(n) = 11 - n for 1 <= n <= 10. Thereafter a(n) = a(n-a(n-2)) + a(n-a(n-4)).

Original entry on oeis.org

10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 6, 8, 10, 15, 8, 13, 6, 14, 16, 9, 14, 13, 6, 14, 22, 18, 20, 16, 6, 23, 28, 15, 26, 22, 6, 29, 34, 15, 32, 28, 6, 35, 40, 15, 38, 34, 6, 41, 46, 15, 44, 40, 6, 47, 52, 15, 50, 46, 6, 53, 58, 15, 56, 52, 6, 59, 64, 15, 62, 58, 6, 65, 70, 15, 68, 64, 6, 71

Offset: 1

Altug Alkan, May 15 2018

Cf. A087777, A240809, A244477, A304490.

f:= proc(n) option remember; procname(n-procname(n-2))+procname(n-procname(n-4)) end proc:
for i from 1 to 10 do f(i):= 11-i od:
map(f, [$1..100]); # Robert Israel, May 16 2018

q=vector(10^5); for(n=1, 10, q[n]=10-n+1); for(n=11, #q, q[n]=q[n-q[n-2]]+ q[n-q[n-4]]); q

a(6*k-3) = 6*(k-1)-4, a(6*k-2) = 6*(k-2)-2, a(6*k-1) = 6, a(6*k) = 6*(k-1)-1, a(6*k+1) = 6*k-2, a(6*k+2) = 15 for k > 4.

cp's OEIS Frontend

A063882 a(n) = a(n - a(n - 1)) + a(n - a(n - 4)), with a(1) = ... = a(4) = 1.

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A240811 a(n) = length (or lifetime) of the meta-Fibonacci sequence f(1) = ... = f(n) = 1; f(k)=f(k-f(k-2))+f(k-f(k-n)) if that sequence is only defined for finitely many terms, or 0 if that sequence is infinite.

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A304490 a(1) = a(2) = a(3) = 1, a(4) = 5, a(5) = 6, a(6) = 4; a(n) = a(n-a(n-2)) + a(n-a(n-4)) for n > 6.

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A304590 a(1) = a(2) = a(3) = a(5) = 1, a(4) = 2, a(6) = 3; a(n) = a(n-a(n-3)) + a(n-a(n-6)) for n > 6.

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A304622 a(n) = 11 - n for 1 <= n <= 10. Thereafter a(n) = a(n-a(n-2)) + a(n-a(n-4)).

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Maple

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