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%I #24 May 31 2017 22:59:34
%S 1,2,2,2,4,4,4,4,6,8,8,6,8,8,8,8,10,14,16,12,14,14,14,16,16,16,16,14,
%T 16,16,16,16,20,26,24,24,24,24,24,24,28,28,22,28,30,30,28,30,32,32,32,
%U 32,30,32,32,32,32,32,32,30,32,32,32,32,40,52,48,42,44,44,44,42,44,44,44,44,52,60,46,54,56,48,54,56,48
%N a(1) = 1, a(2) = a(3) = a(4) = 2; a(n) = a(a(n-1)) + a(a(n-a(n-1)) + a(n-a(n-2))) for n > 4.
%C There are substantial jumps between generations (i.e. a(2^19) = 2^18 and a(2^19 + 1) = 327608). See also scatterplot in links section.
%H Altug Alkan, <a href="/A287654/a287654_1.png">Scatterplot of a(n)</a>
%H <a href="/index/Ho#Hofstadter">Index entries for Hofstadter-type sequences</a>
%p N:= 2^10: # to get a(1) to a(N)
%p C[1]:= 1:
%p C[2]:= 2:
%p C[3]:= 2:
%p C[4]:= 2:
%p for n from 5 to N do
%p C[n]:= C[C[n-1]] + C[C[n-C[n-1]] + C[n-C[n-2]]];
%p od:
%p S:=seq(C[n], n=1..N);
%o (Scheme)
%o ;; An implementation of memoization-macro definec can be found for example in: http://oeis.org/wiki/Memoization
%o (definec (A287654 n) (cond ((= 1 n) n) ((<= n 4) 2) (else (+ (A287654 (A287654 (- n 1))) (A287654 (+ (A287654 (- n (A287654 (- n 1)))) (A287654 (- n (A287654 (- n 2)))))))))) ;; _Antti Karttunen_, May 31 2017
%Y Cf. A004001, A005185, A287292, A287707.
%K nonn
%O 1,2
%A _Altug Alkan_, May 30 2017
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