%I
%S 1,2,4,7,44,47,74,77,444,447,474,477,744,747,774,777,4444,4447,4474,
%T 4477,4744,4747,4774,4777,7444,7447,7474,7477,7744,7747,7774,7777,
%U 44444,44447,44474,44477,44744,44747,44774,44777,47444,47447,47474,47477,47744,47747,47774,47777,74444,74447
%N Lexicographically first sequence of distinct terms such that the sum of any two terms is not a term of the sequence, and the sum of any two digits is not a digit of the sequence.
%C The full sequence uses digits 4 and 7 only, except for a(1) = 1 and a(2) = 2.
%H JeanMarc Falcoz, <a href="/A302938/b302938.txt">Table of n, a(n) for n = 1..16384</a>
%e 1 + 2 = 3 and there is no term or digit 3 in the sequence;
%e 1 + 4 = 5 and there is no term or digit 5 in the sequence;
%e 1 + 7 = 8 and there is no term or digit 8 in the sequence;
%e 2 + 4 = 6 and there is no term or digit 6 in the sequence;
%e 2 + 7 = 9 and there is no term or digit 9 in the sequence;
%e 4 + 4 = 8 and there is no term or digit 8 in the sequence;
%e 4 + 7 = 11 and there is no term 11 in the sequence;
%e 7 + 7 = 14 and there is no term 14 in the sequence;
%e etc.
%Y Cf. A302940 where the word “sum” is replaced by “product”.
%Y Cf. A014261 which shares the same property (numbers that contain odd digits only).
%Y Cf. A284971.
%K nonn,base
%O 1,2
%A _Eric Angelini_ and _JeanMarc Falcoz_, Apr 16 2018
