[seqfan] Another Subset of A152824

[zak seidov]

%I A152853
%S A152853 337,737,7373,73333,73733,333377,333733,737333,737773,777337,777737,
%T A152853 3333373,3333773,3373337,3373777,3777377,3777733,7337737,7373333,
%U A152853 7373773,7733377,7733777,7777373,33337333,33337733,33377737,33733373
%N A152853 Numbers of form 21k+1 or 21k+2 that use only digits 3 and 7. 
%Y A152853 Subset of A152824. Cf. A152834 for case of digits 2 and 3. 
%K A152853 base,nonn
%O A152853 1,1
%A A152853 Zak Seidov (zakseidov(AT)yahoo.com), Dec 14 2008