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%I #7 Sep 20 2022 16:14:01
%S 3,9,33,39,93,99,333,339,393,399,933,939,993,999,3333,3339,3393,3399,
%T 3933,3939,3993,3999,9333,9339,9393,9399,9933,9939,9993,9999,33333,
%U 33339,33393,33399,33933,33939,33993,33999,39333,39339,39393,39399,39933,39939
%N Numbers with digits 3 and 9 only.
%C All terms > 3 are composite.
%F a(n) = 3 * A032917(n).
%t Table[FromDigits/@Tuples[{3,9},n],{n,5}]//Flatten (* _Harvey P. Dale_, Sep 20 2022 *)
%o (Magma) [n: n in [1..100000] | Set(IntegerToSequence(n, 10)) subset {3, 9}]
%Y Cf. Numbers with digits 3 and k only for k = 0 - 2 and 4 - 9: A169966 (k = 0), A032917 (k = 1), A032810 (k = 2), A032834 (k = 4), A284379 (k = 5), A284633 (k = 6), A143967 (k = 7), A284963 (k = 8), this sequence (k = 9).
%K nonn,base
%O 1,1
%A _Jaroslav Krizek_, Apr 06 2017