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%I #7 Mar 30 2012 17:23:02
%S 4,16,20,37,42,58,89,145,78999,79899,79989,79998,87999,89799,89979,
%T 89997,97899,97989,97998,98799,98979,98997,99789,99798,99879,99897,
%U 99978,99987,378999,379899,379989,379998,387999,389799,389979,389997,389999,397899,397989
%N Numbers that require exactly 8 iterations to determine that they are happy or not (A007770 and A031177).
%C This sequence begins with the last 8 numbers of A039943. The number 78999 is the first happy number here.
%t f[n_] := Total[IntegerDigits[n]^2]; Select[Range[400000], Length[NestWhileList[f, #, UnsameQ, All]] - 1 == 8 &]
%K nonn,base
%O 1,1
%A _T. D. Noe_, Aug 23 2011