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A046439 9 steps needed to reach a prime under "Sum of digits raised to its digits' powers" procedure. 2

%I

%S 133,138,183,303,308,313,318,330,331,380,381,389,398,446,464,644,789,

%T 798,803,813,830,831,839,879,893,897,938,978,983,987,1005,1015,1024,

%U 1042,1046,1050,1051,1064,1105,1115,1124,1142,1146,1150,1151,1164,1204

%N 9 steps needed to reach a prime under "Sum of digits raised to its digits' powers" procedure.

%t sop[n_] := Total[#^# & /@ (IntegerDigits[n] /. {0 -> 1})]; Select[Range[1205], (z = Boole /@ PrimeQ[Rest[NestList[sop, #, 9]]])[[9]] - Total[Drop[z, -1]] == 1 &] (* _Jayanta Basu_, Jun 25 2013 *)

%Y Cf. A046431.

%K nonn,base

%O 0,1

%A _Patrick De Geest_, Jul 15 1998

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Last modified June 19 13:04 EDT 2021. Contains 345129 sequences. (Running on oeis4.)