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A072204
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a(n) is the smallest integer k whose factorial contains exactly n 7's, or 0 if no such number exists.
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9
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6, 14, 18, 31, 49, 22, 54, 48, 56, 71, 82, 72, 86, 81, 92, 97, 87, 122, 91, 119, 131, 112, 121, 140, 104, 152, 144, 173, 127, 157, 172, 201, 227, 179, 200, 187, 183, 210, 236, 221, 193, 217, 279, 212, 213, 235, 238, 289, 265, 228, 256, 261, 250, 242, 285, 307
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(2) = 14 since the 14th factorial, i.e., 14! = 87178291200, contains exactly two 7's.
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MATHEMATICA
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Do[k = 1; While[ Count[IntegerDigits[k! ], 7] != n, k++ ]; Print[k], {n, 1, 60}]
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PROG
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(Python)
def a(n, bound=10**4):
k = f = 1
while not str(f).count('7') == n and k <= bound: k += 1; f *= k
return k * (k <= bound)
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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