id:A078680 - OEIS Search Results

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Start with n; repeatedly double and subtract 1 until reach a prime. Sequence gives number of steps to reach a prime or 0 if no prime is ever reached.

+0
1

1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 3, 2, 1, 1, 4, 3, 1, 6, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 8, 3, 1, 2, 1, 1, 2, 5, 1, 4, 1, 3, 2, 1, 2, 8, 583, 1, 2, 1, 1, 6, 1, 1, 4, 1, 2, 2, 5, 2, 4, 7, 1, 2, 1, 5, 2, 1, 1, 2, 3, 3, 2, 1, 1, 4, 3, 1, 2, 3, 1, 10, 1, 2, 4, 1, 2, 2, 1, 1, 8, 7, 2, 582, 1, 1, 2, 1, 1, 2, 3, 2 (list; graph; listen)

	OFFSET	`2,4`
	PROGRAM	`(PARI) a(n)=if(n<0, 0, s=n; c=1; while(isprime(2s-1)==0, s=2s-1; c++); c)`
	CROSSREFS	`Cf. A050412.` `Sequence in context: A076845 A016014 A067760 this_sequence A050412 A025898 A025849` `Adjacent sequences: A078677 A078678 A078679 this_sequence A078681 A078682 A078683`
	KEYWORD	`nonn`
	AUTHOR	`Benoit Cloitre (benoit7848c(AT)orange.fr), Dec 17 2002`

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Last modified July 26 23:19 EDT 2008. Contains 142293 sequences.

AT&T Labs Research