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A284520 a(1) = 1, a(2) = a(3) = a(4) = 2; a(n) = a(a(n-1)-1) + a(n-a(n-3)-1) for n > 4.

%I A284520 #11 Apr 01 2017 07:47:56
%S A284520 1,2,2,2,3,4,4,4,4,5,6,7,8,8,8,8,8,8,9,10,11,12,13,14,15,15,15,15,16,
%T A284520 16,16,16,16,16,16,17,18,19,19,19,19,20,22,25,28,28,26,24,23,25,29,30,
%U A284520 31,30,30,30,31,31,31,31,32,32,32,32,32,32,32,32,33,34,35,35,35
%N A284520 a(1) = 1, a(2) = a(3) = a(4) = 2; a(n) = a(a(n-1)-1) + a(n-a(n-3)-1) for n > 4.
%H A284520 Altug Alkan, <a href="/A284520/b284520.txt">Table of n, a(n) for n = 1..20000</a>
%H A284520 Altug Alkan, <a href="/A284520/a284520.png">Scatterplot of A284520</a>
%e A284520 a(5) = 3 because a(5) = a(a(4)-1) + a(5-a(2)-1) = a(1) + a(2) = 3.
%o A284520 (PARI) a=vector(1000); 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]-1]); a
%Y A284520 Cf. A004001, A005185, A005229, A055748, A070867, A226222, A284511.
%K A284520 nonn,look
%O A284520 1,2
%A A284520 _Altug Alkan_, Mar 28 2017