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return 0 if max(pf) > 7 else int(''.join(sorted(''.join(str(a)*(n*b) for a, b in pf.items()).replace('222', '8').replace('22', '4').replace('33', '9')))) # Chai Wah Wu, Aug 13 2017
(Python)
from sympy import factorint
def A068187(n):
if n == 1:
return 1
pf = factorint(n)
return 0 if max(pf) > 7 else int(''.join(sorted(''.join(str(a)*(n*b) for a, b in pf.items()).replace('222', '8').replace('22', '4').replace('33', '9')))) # Chai Wah Wu, Aug 13 2017
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1, 4, 39, 488, 55555, 88999, 7777777, 88888888, 999999999, 25555555555888, 0, 88888888999999, 0, 4777777777777778888, 35555555555555559999999, 2888888888888888888888, 0, 888888999999999999999999, 0, 2555555555555555555558888888888888, 37777777777777777777779999999999
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Chai Wah Wu, <a href="/A068187/b068187_1.txt">Table of n, a(n) for n = 1..200</a>
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