A046438 Numbers from which 8 steps are needed to reach a prime under "Sum of digits raised to its digits' powers" procedure.

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

Offset

1,1

Comments

0^0 is treated as 1. - Harvey P. Dale, Mar 06 2013

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Mathematica

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 *)

Prog

(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

Crossrefs

Cf. A046431.

Sequence in context: A096664 A067978 A072429 * A043510 A044387 A044768

Adjacent sequences: A046435 A046436 A046437 * A046439 A046440 A046441

Keyword

nonn,base

Author

Patrick De Geest, Jul 15 1998

Status

approved