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Search: id:A120716
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| A120716 |
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a(1)=1, a(p)=p if p is a prime. Otherwise, start with n, and iterate the map (k -> concatenation of proper divisors of k) until we reach a prime q; then a(n) = q. If we never reach a prime, a(n) = -1. |
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7
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OFFSET
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1,2
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LINKS
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N. J. A. Sloane et al., Notes on the attempt to find a(8)
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EXAMPLE
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4 -> 2, prime, so a(4) = 2.
6 -> 2,3 -> 23, prime, so a(6) = 23.
8 -> 2.4 -> 24 -> 2.3.4.6.8.12 -> 2346812 -> 2.4.13.26.52.45131.90262.180524.586703.1173406 -> 2413265245131902621805245867031173406 -> ? (see link for the continuation)
9 -> 3, prime, so a(9) = 3.
21 -> 3,7 -> 37, prime, so a(21) = 37.
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CROSSREFS
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Cf. A120712, A120713, A037274, A130139-A130142. A130139 is a bisection.
Adjacent sequences: A120713 A120714 A120715 this_sequence A120717 A120718 A120719
Sequence in context: A010242 A086507 A133568 this_sequence A084318 A084317 A037279
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KEYWORD
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nonn,base,more,hard
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AUTHOR
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njas, Jul 19 2007
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EXTENSIONS
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a(8) is currently unknown.
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