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A284380 Numbers k with digits 5 and 7 only.

%I A284380 #19 Jun 25 2025 14:36:40
%S A284380 5,7,55,57,75,77,555,557,575,577,755,757,775,777,5555,5557,5575,5577,
%T A284380 5755,5757,5775,5777,7555,7557,7575,7577,7755,7757,7775,7777,55555,
%U A284380 55557,55575,55577,55755,55757,55775,55777,57555,57557,57575,57577,57755,57757
%N A284380 Numbers k with digits 5 and 7 only.
%H A284380 Michael S. Branicky, <a href="/A284380/b284380.txt">Table of n, a(n) for n = 1..10000</a>
%t A284380 Join @@ ((FromDigits /@ Tuples[{5, 7}, #]) & /@ Range@ 5) (* _Giovanni Resta_, Mar 28 2017 *)
%o A284380 (Magma) [n: n in [1..100000] | Set(IntegerToSequence(n, 10)) subset {5, 7}];
%o A284380 (Python)
%o A284380 from sympy.utilities.iterables import multiset_permutations
%o A284380 def aupton(terms):
%o A284380   n, digits, alst = 0, 1, []
%o A284380   while len(alst) < terms:
%o A284380     mpstr = "".join(d*digits for d in "57")
%o A284380     for mp in multiset_permutations(mpstr, digits):
%o A284380       alst.append(int("".join(mp)))
%o A284380       if len(alst) == terms: break
%o A284380     else: digits += 1
%o A284380   return alst
%o A284380 print(aupton(44)) # _Michael S. Branicky_, May 07 2021
%Y A284380 Prime terms are in A020467.
%Y A284380 Numbers n with digits 5 and k only for k = 0 - 4 and 6 - 9: A169964 (k = 0), A276037 (k = 1), A072961 (k = 2), A284379 (k = 3), A256290 (k = 4), A256291 (k = 6), this sequence (k = 7), A284381 (k = 8), A284382 (k = 9).
%K A284380 nonn,base
%O A284380 1,1
%A A284380 _Jaroslav Krizek_, Mar 28 2017