%I A129751
%S A129751 0,102,101022,101021010222,101021010221010210102222,
%T A129751 101021010221010210102221010210102210102101022222,
%U A129751 101021010221010210102221010210102210102101022221010210102210102101022210102101022101021010222222
%N A129751 The natural numbers represented by their set theoretic Von Neumann construction, 
               where the empty set is replaced by '0', the left set bracket '{' 
               is replaced by 1, the right bracket '}' is replaced by 2 and the 
               set construct contents are ordered by increasing cardinality.
%C A129751 Other sequences may be obtained by using different substitutions for 
               '0', '{' and '}'.
%D A129751 http://planetmath.org/encyclopedia/VonNeumannInteger.html
%H A129751 I.N. Galidakis, <a href="http://ioannis.virtualcomposer2000.com/">Home 
               Page</a>
%F A129751 S(n)=n union {n}
%e A129751 a(0)=0, a(1)={0}=102, a(2)={0,{0}}=101022, etc.
%p A129751 N:=proc(n) local i,s,l,r,data; s:=`0`;l:=`1`;r:=`2`; #change here for 
               different sequences if n>0 then for i from 1 to n-1 do s:=cat(s,l,
               s,r); od; s:=cat(l,s,r); fi; data:=sscanf(s,`%d`); RETURN(data[1]); 
               end:
%Y A129751 Cf. A129754.
%Y A129751 Sequence in context: A163435 A030512 A097725 this_sequence A094095 A074675 
               A161402
%Y A129751 Adjacent sequences: A129748 A129749 A129750 this_sequence A129752 A129753 
               A129754
%K A129751 easy,nonn
%O A129751 0,2
%A A129751 I.N. Galidakis (jgal(AT)ath.forthnet.gr), May 14 2007