OFFSET
1,2
COMMENTS
Although sequence is unpredictable with its complex growth characteristic and generational structure, it has various signs of order and there are many temporary and simple patterns on it. For example, values of a(n) such that a(n) = a(n + 1) = a(n + 2) = a(n + 3) are 5, 10, 20, 40, 80, 160, 320, 640, 1280, ...
LINKS
Altug Alkan, Table of n, a(n) for n = 1..10000
Altug Alkan, Alternative scatterplot of A285509
EXAMPLE
a(5) = 3 because a(5) = a(a(4)-1) + a(5-a(2)) = a(1) + a(3) = 2.
MATHEMATICA
a[1]=1; a[2]=a[3]=a[4]=2; a[n_] := a[n] = a[a[n-1]-1] + a[n-a[n-3]]; Array[a, 84] (* Giovanni Resta, Apr 21 2017 *)
PROG
(PARI) a=vector(10000); a[1]=1; a[2]=a[3]=a[4]=2; for(n=5, #a, a[n]=a[a[n-1]-1]+a[n-a[n-3]]); va = vector(10000, n, a[n])
CROSSREFS
KEYWORD
nonn,look
AUTHOR
Altug Alkan, Apr 20 2017
STATUS
approved