id:A050412 - OEIS Search Results

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Riesel problem: start with n; repeatedly double and add 1 until reach a prime. Sequence gives number of steps to reach a prime or 0 if no prime is ever reached.

+0
12

1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 3, 4, 1, 1, 2, 2, 1, 2, 1, 1, 4, 1, 3, 2, 1, 3, 4, 1, 1, 2, 2, 1, 2, 1, 1, 2, 3, 1, 2, 1, 7, 24, 1, 3, 4, 2, 1, 2, 1, 1, 2, 1, 1, 2, 1, 3, 12, 2, 3, 4, 2, 1, 4, 1, 5, 2, 1, 1, 2, 4, 7, 2552, 1, 1, 2, 2, 1, 4, 3, 1, 2, 1, 5, 6, 1, 23, 4, 1, 1, 2, 3, 3, 2, 1, 1, 4, 1, 1 (list; graph; listen)

	OFFSET	`1,4`
	COMMENT	`a(n) = smallest m >= 1 such that n*2^m - 1 is prime (or 0 if no such prime exists).`
	LINKS	`T. D. Noe, Table of n, a(n) for n=1..657` `Ray Ballinger and Wilfrid Keller, The Riesel Problem: Definition and Status`
	PROGRAM	`(PARI) a(n)=if(n<0, 0, s=n; c=1; while(isprime(2s+1)==0, s=2s+1; c++); c)`
	CROSSREFS	`Cf. A051914, A052333 (primes reached), A052334, A052339, A052340, A050413.` `Sequence in context: A016014 A067760 A078680 this_sequence A025898 A025849 A088782` `Adjacent sequences: A050409 A050410 A050411 this_sequence A050413 A050414 A050415`
	KEYWORD	`nonn,nice,easy`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 22 1999`
	EXTENSIONS	`More terms from Christian G. Bower (bowerc(AT)usa.net), Dec 23 1999`

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Last modified July 25 07:41 EDT 2008. Contains 142293 sequences.

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