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A109931
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Least palindromic multiple of concatenation n,n-1,...,3,2,1,2,3,...,n-1,n, or zero if no such multiple exists. a(n) is not equal to n.
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1
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OFFSET
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1,1
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COMMENTS
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The multipliers are: 2, 2, 2, 2, 11, 1001, 100001, 10000001, ...
Such a multiple may fail to exist for n >= 10 because the concatenation n,n-1,...,3,2,1,2,3,...,n-1,n is no longer a palindrome itself in that case (e.g., for n=10 the concatenation is 109876543212345678910). - Nathaniel Johnston, Jun 26 2011
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LINKS
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EXAMPLE
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a(5) = 5975335795 = 11*543212345.
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MAPLE
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read(transforms): A109931 := proc(n) local k, m, v: m:=parse(cat(digrev(parse(cat($(1..n)))), cat($(2..n)))): for k from 2 do v:=k*m: if(v=digrev(v))then return v: fi: od: end: seq(A109931(n), n=2..6); # only valid for n <= 9, Nathaniel Johnston, Jun 26 2011
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CROSSREFS
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KEYWORD
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base,more,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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