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A151962
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Length of preperiodic part of trajectory of n under iteration of the Kaprekar map in A151949.
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11
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0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 6, 4, 5, 3, 3, 5, 4, 6, 2, 1, 2, 6, 4, 5, 3, 3, 5, 4, 6, 2, 1, 2, 6, 4, 5, 3, 3, 5, 4, 6, 2, 1, 2, 6, 4, 5, 3, 3, 5, 4, 6, 2, 1, 2, 6, 4, 5, 3, 3, 5, 4, 6, 2, 1, 2, 6, 4, 5, 3, 3, 5, 4, 6, 2, 1, 2, 6, 4, 5, 3, 3, 5, 4, 6, 2, 1, 2, 6, 4, 5, 3, 3, 5, 4, 6, 2
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OFFSET
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0,11
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LINKS
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EXAMPLE
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13 -> 18 -> 63 -> 27 -> 45 -> 9 -> 0 -> 0, so a(13)=6.
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MAPLE
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local tup;
tup := sort(convert(n, base, 10)) ;
add( (op(i, tup)-op(-i, tup)) *10^(i-1), i=1..nops(tup)) :
end:
local tra, x ;
tra := [n] ;
x := n ;
while true do
if member(x, tra, 'l') then
RETURN(l-1) ;
fi;
tra := [op(tra), x] :
od:
end:
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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