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A103160
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a(n) = GCD(reverse(n!), reverse((n+1)!)).
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0
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1, 2, 6, 21, 3, 27, 9, 9, 88263, 9, 99, 594, 198, 99, 99, 99, 99, 99, 99, 9009, 99, 99, 198, 99, 99, 297, 1089, 99, 198, 198, 594, 198, 396, 693, 99, 99, 99, 297, 594, 99, 99, 99, 198, 99, 99, 99, 99, 99, 99, 99, 99, 396, 2772, 99, 99, 99, 396, 693, 693, 99, 99, 99, 99
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graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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COMMENTS
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Through the first 200 terms, the largest term has 6 digits with the exception of a(99) which has 134 digits. - Harvey P. Dale, Dec 24 2018
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LINKS
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FORMULA
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EXAMPLE
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Outstandingly high values arise at n = 10^k - 1 because
See n = 9, 99, 999, etc.
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MATHEMATICA
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rd[x_] :=FromDigits[Reverse[IntegerDigits[x]]] Table[GCD[rd[w! ], rd[(w+1)! ]], {w, 1, 100}]
GCD@@#&/@Partition[IntegerReverse[Range[100]!], 2, 1] (* Harvey P. Dale, Dec 24 2018 *)
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PROG
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(Python)
from math import factorial, gcd
def a(n):
f = factorial(n)
return gcd(int(str(f)[::-1]), int(str(f*(n+1))[::-1]))
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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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