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A173558
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a(n) is the smallest number whose factorial has 10^n trailing zeros.
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3
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5, 45, 405, 4005, 40010, 400005, 4000005, 40000010, 400000015, 4000000015, 40000000015, 400000000015, 4000000000010, 40000000000015, 400000000000020, 4000000000000025, 40000000000000025, 400000000000000025
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OFFSET
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0,1
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LINKS
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EXAMPLE
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4!=24 has no zeros, and 5!=120 has 1 (10^0) zero ==> a(0)= 5.
44!=2658271574788448768043625811014615890319638528000000000 (9 zeros) and 45!=119622220865480194561963161495657715064383733760000000000 (10^1= 10 zeros) ==> a(1)=45.
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MATHEMATICA
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Z10[n_] := Floor[Sum[Floor[n/5^i], {i, 1, Floor[Log[5, n]]}]]; a[n_] := Module[{m = 4*10^n}, While[Z10[m] < 10^n, m++ ]; m]; Table[a[n], {n, 0, 60}]
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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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STATUS
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approved
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