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A046438
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Numbers from which 8 steps are needed to reach a prime under "Sum of digits raised to its digits' powers" procedure.
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2
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55, 155, 226, 244, 247, 255, 262, 274, 424, 427, 442, 472, 505, 515, 525, 550, 551, 552, 622, 724, 742, 1039, 1093, 1139, 1193, 1234, 1238, 1243, 1283, 1309, 1319, 1324, 1328, 1342, 1382, 1390, 1391, 1423, 1432, 1823, 1832, 1903, 1913, 1930, 1931
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OFFSET
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1,1
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COMMENTS
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LINKS
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MATHEMATICA
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nxt[n_]:=Module[{idn=IntegerDigits[n]/.{0->1}}, Total[idn^idn]]; Select[ Range[ 2000], Rest[PrimeQ[NestList[nxt, #, 8]]]=={False, False, False, False, False, False, False, True}&] (* Harvey P. Dale, Mar 06 2013 *)
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PROG
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(PARI) is(n)=for(i=1, 8, if(i>1&&isprime(n), return(0)); n=digits(n); n= sum(i=1, #n, n[i]^n[i])); isprime(n) \\ Charles R Greathouse IV, Mar 06 2013
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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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STATUS
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approved
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