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a(1) = 8127; thereafter a(n) = (a(n-1) with digits sorted into descending order) - (a(n-1) with digits sorted into ascending order) (see the Kaprekar map, A151949).
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%I #5 Mar 30 2012 16:51:07

%S 8127,7443,3996,6264,4176,6174,6174,6174,6174,6174,6174,6174,6174,

%T 6174,6174,6174,6174,6174,6174,6174,6174,6174,6174,6174,6174,6174,

%U 6174,6174,6174,6174,6174,6174,6174,6174,6174,6174,6174,6174,6174

%N a(1) = 8127; thereafter a(n) = (a(n-1) with digits sorted into descending order) - (a(n-1) with digits sorted into ascending order) (see the Kaprekar map, A151949).

%C Similar in spirit to the RATS (Reverse, Add Then Sort) sequences.

%C Converges to the fixed point 6174. For the list of fixed points see A099009.

%C The initial value 1001 is the smallest number that converges to 6174 - see A151967.

%H John Tierney, <a href="http://nytimes.com/tierneylab">"TierneyLab" column, New York Times, Section C, Aug 18 2009</a>

%H <a href="/index/K#Kaprekar_map">Index entries for the Kaprekar map</a>

%H <a href="/index/Ra#RATS">Index entries for RATS sequences</a>

%Y Cf. A099009, A151947, A151949, A151951, A151955, A151956, A151967. A151968.

%K nonn,base

%O 1,1

%A _N. J. A. Sloane_, Aug 18 2009