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 A037273 Number of steps to reach a prime under "replace n with concatenation of its prime factors", or -1 if no such number. 30
 -1, 0, 0, 2, 0, 1, 0, 13, 2, 4, 0, 1, 0, 5, 4, 4, 0, 1, 0, 15, 1, 1, 0, 2, 3, 4, 4, 1, 0, 2, 0, 2, 1, 5, 3, 2, 0, 2, 1, 9, 0, 2, 0, 9, 6, 1, 0, 15 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 LINKS P. De Geest, Home Primes Eric Weisstein's World of Mathematics, Home Prime EXAMPLE 13 is already prime, so a(13) = 0. Starting with 14 we get 14 = 2*7, 27 = 3*3*3, 333 = 3*3*37, 3337 = 47*71, 4771 = 13*367, 13367 is prime; so a(14) = 5. MATHEMATICA nxt[n_] := FromDigits[Flatten[IntegerDigits/@Table[#[[1]], {#[[2]]}]&/@ FactorInteger[n]]]; Table[Length[NestWhileList[nxt, n, !PrimeQ[#]&]] - 1, {n, 48}] (* Harvey P. Dale, Jan 03 2013 *) PROG (Haskell) a037273 1 = -1 a037273 n = length \$ takeWhile ((== 0) . a010051) \$    iterate (\x -> read \$ concatMap show \$ a027746_row x :: Integer) n -- Reinhard Zumkeller, Jan 08 2013 CROSSREFS Cf. A037271-A037275, A056938. Cf. A010051, A027746. Sequence in context: A049218 A212358 A154469 * A285313 A231366 A158924 Adjacent sequences:  A037270 A037271 A037272 * A037274 A037275 A037276 KEYWORD sign,nice,hard,base AUTHOR EXTENSIONS Starting with 49, no prime has been reached after 79 steps. Edited by Charles R Greathouse IV, Apr 23 2010 a(1) = -1 by Reinhard Zumkeller, Jan 08 2013 STATUS approved

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Last modified December 16 19:11 EST 2018. Contains 318188 sequences. (Running on oeis4.)