A287707 - OEIS

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A287707

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

1, 2, 3, 2, 2, 4, 4, 4, 4, 6, 8, 8, 6, 8, 8, 8, 8, 12, 16, 12, 12, 16, 16, 12, 14, 16, 16, 16, 16, 16, 16, 16, 16, 20, 24, 20, 20, 24, 24, 20, 24, 28, 28, 24, 24, 28, 32, 28, 28, 32, 32, 28, 32, 32, 32, 28, 32, 32, 32, 32, 32, 32, 32, 32, 32, 36, 40, 36, 36, 40, 40, 36, 40, 44, 44, 40, 40, 48, 48, 44, 44, 52, 48

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

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

Altug Alkan, Plot of a(n)-n/2

Indranil Ghosh, Python program to compute the sequence

Index entries for Hofstadter-type sequences

MAPLE

N:= 2^10: # to get a(1) to a(N)

C[1]:= 1:

C[2]:= 2:

C[3]:= 3:

C[4]:= 2:

C[5]:= 2:

for n from 6 to N do

C[n]:= C[C[n-1]] + C[C[n-C[n-1]] + C[n-C[n-2]]];

od:

S:=seq(C[n], n=1..N);

PROG

(Scheme)

;; An implementation of memoization-macro definec can be found for example in: http://oeis.org/wiki/Memoization

(definec (A287707 n) (cond ((or (= 1 n) (= 3 n)) n) ((<= n 5) 2) (else (+ (A287707 (A287707 (- n 1))) (A287707 (+ (A287707 (- n (A287707 (- n 1)))) (A287707 (- n (A287707 (- n 2)))))))))) ;; Antti Karttunen, May 31 2017

CROSSREFS

Cf. A004001, A005185, A287654.

Sequence in context: A098534 A317638 A002307 * A029247 A194020 A372053

Adjacent sequences: A287704 A287705 A287706 * A287708 A287709 A287710

KEYWORD

nonn

AUTHOR

Altug Alkan, May 30 2017

STATUS

approved