login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual appeal: Please make a donation to keep the OEIS running! Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A120716 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. 10
1, 2, 3, 2, 5, 23, 7 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..7.

N. J. A. Sloane et al., Notes on the attempt to find a(8)

EXAMPLE

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.

CROSSREFS

Cf. A120712, A120713, A037274, A130139-A130142. A130139 is a bisection.

Sequence in context: A010242 A086507 A133568 * A084318 A084317 A037279

Adjacent sequences:  A120713 A120714 A120715 * A120717 A120718 A120719

KEYWORD

nonn,base,more,hard

AUTHOR

N. J. A. Sloane, Jul 19 2007

EXTENSIONS

a(8) is currently unknown.

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified December 13 09:05 EST 2017. Contains 295957 sequences.