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A037271
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Number of steps to reach a prime under "replace n by concatenation of its prime factors", when applied to n-th composite number, or -1 if no such number.
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20
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2, 1, 13, 2, 4, 1, 5, 4, 4, 1, 15, 1, 1, 2, 3, 4, 4, 1, 2, 2, 1, 5, 3, 2, 2, 1, 9, 2, 9, 6, 1, 15
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| P. De Geest, Home Primes
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
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EXAMPLE
| Starting with 14 (the seventh composite number) we get 14=2*7, 27=3*3*3, 333=3*3*37, 3337=47*71, 4771=13*367, 13367 is prime; so a(7)=5.
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CROSSREFS
| Cf. A037271-A037274, A056938.
Sequence in context: A171510 A124916 A007418 * A074955 A143663 A064079
Adjacent sequences: A037268 A037269 A037270 * A037272 A037273 A037274
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KEYWORD
| nonn,nice,base,hard
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AUTHOR
| Jeff Burch (gburch(AT)erols.com)
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EXTENSIONS
| Starting with 49, no prime has been reached after 79 steps.
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