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 A020467 Primes that contain digits 5 and 7 only. 9
 5, 7, 557, 577, 757, 5557, 7577, 7757, 57557, 75557, 75577, 77557, 555557, 575557, 575777, 577757, 757577, 775757, 775777, 5555777, 5557757, 5575777, 5577577, 5755577, 5775557, 5777557, 7575577, 7577777, 55555777, 55575757, 55755757, 55757777, 57557557 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 MATHEMATICA Flatten[Table[Select[FromDigits/@Tuples[{5, 7}, n], PrimeQ], {n, 8}]] PROG (Magma) [p: p in PrimesUpTo(55755757 ) | Set(Intseq(p)) subset [5, 7]]; // Vincenzo Librandi, Jul 27 2012 (Python) from sympy import isprime from sympy.utilities.iterables import multiset_permutations def aupton(terms): n, digits, alst = 0, 1, [] while len(alst) < terms: mpstr = "".join(d*digits for d in "57") for mp in multiset_permutations(mpstr, digits): t = int("".join(mp)) if isprime(t): alst.append(t) if len(alst) == terms: break else: digits += 1 return alst print(aupton(33)) # Michael S. Branicky, May 07 2021 CROSSREFS Subsequence of A260827-A260831 and A284380. Sequence in context: A114368 A260830 A260827 * A089344 A114363 A083687 Adjacent sequences: A020464 A020465 A020466 * A020468 A020469 A020470 KEYWORD nonn,base AUTHOR David W. Wilson STATUS approved

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Last modified June 1 18:23 EDT 2023. Contains 363076 sequences. (Running on oeis4.)