A120716 - OEIS

This site is supported by donations to The OEIS Foundation.

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.

1, 2, 3, 2, 5, 23, 7 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	LINKS	`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 (njas(AT)research.att.com), Jul 19 2007`
	EXTENSIONS	`a(8) is currently unknown.`

Content is available under The OEIS End-User License Agreement .

Last modified February 13 12:58 EST 2012. Contains 205482 sequences.