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A020467
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Primes that contain digits 5 and 7 only.
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9
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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
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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Flatten[Table[Select[FromDigits/@Tuples[{5, 7}, n], PrimeQ], {n, 8}]]
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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