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A309596 If a(n) is not a term of a(0..n-1), then a(n+1) = a(n) - a(n - a(n)); otherwise a(n+1) is the number of terms equal to a(n) in a(0..n-1). Start with a(0)=0, a(1)=0. 0
0, 0, 1, 1, 1, 2, 1, 3, 2, 1, 4, 3, 1, 5, 3, 2, 2, 3, 3, 4, 1, 6, 4, 2, 4, 3, 5, 1, 7, 1, 8, 4, 4, 5, 2, 5, 3, 6, 1, 9, 1, 10, 6, 2, 6, 3, 7, 1, 11, 5, 4, 6, 4, 7, 2, 7, 3, 8, 1, 12, 11, 1, 13, 8, 2, 8, 3, 9, 1, 14, 7, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,6

COMMENTS

In other words, if the last term a(n) has not appeared previously, subtract the term a(n - a(n)) from a(n) to get the next term. Otherwise, count the terms equal to the last term a(n) in a(0..n-1) to get the next term.

This sequence has no repeating pattern because of the rule a(n+1) = a(n) - a(n - a(n)).

A new record in the sequence is always the previous record + 1. Therefore all terms are >= 0.

LINKS

Table of n, a(n) for n=0..71.

EXAMPLE

a(0)=0 (given).

a(1)=0 (given).

a(2)=1: a(1)=0 is a term of a(0..0), therefore a(2) = Number of terms=0 in a(0..0) = 1.

a(3)=1: a(2)=1 is not a term of a(0..1), therefore: a(3) = a(2) - a(2 - 1) = 1 - 0 = 1.

a(4)=1: a(3)=1 is a term of a(0..2), therefore a(4) = Number of terms=1 in a(0..2) = 1.

a(5)=2: a(4)=1 is a term of a(0..3), therefore a(5) = Number of terms=1 in a(0..3) = 2.

a(6)=1: a(5)=2 is not a term of a(0..4), therefore: a(6) = a(5) - a(5 - 2) = 2 - 1 = 1.

MATHEMATICA

s={0, 0}; Do[s1 = If[(c = Count[s[[1;; -2]], s[[-1]]]) == 0, s[[-1]] - s[[-1 -  s[[-1]]]], c]; AppendTo[s, s1], {100}]; s (* Amiram Eldar, Aug 13 2019 *)

PROG

(Python)

sa, n = [0], 0

print(n, sa[n])

while n < 50:

    i, j = 0, 0

    while i < n:

        if sa[i] == sa[n]:

            j = j+1

        i = i+1

    if j == 0:

        a = sa[n] - sa[n-sa[n]]

    else:

        a = j

    n = n+1

    print(n, a)

    sa = sa+[a] # A.H.M. Smeets, Aug 09 2019

CROSSREFS

Cf. A181391, A309035.

Sequence in context: A278104 A141672 A141671 * A226247 A233742 A194856

Adjacent sequences:  A309593 A309594 A309595 * A309597 A309598 A309599

KEYWORD

nonn

AUTHOR

Marc Morgenegg, Aug 09 2019

STATUS

approved

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Last modified April 3 21:54 EDT 2020. Contains 333207 sequences. (Running on oeis4.)