This site is supported by donations to The OEIS Foundation.

 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!)
 A140525 a(1)=2. For n >=2, a(n) = the least integer >= a(n-1) that is not coprime to both a(n-1)+1 and a(n-1). 1
 2, 6, 14, 18, 38, 42, 86, 90, 98, 102, 206, 210, 422, 426, 434, 438, 878, 882, 1766, 1770, 1778, 1782, 3566, 3570, 7142, 7146, 7154, 7158, 14318, 14322, 28646, 28650, 28658, 28662, 57326, 57330, 114662, 114666, 114674, 114678, 229358, 229362, 229400 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also: a(n+1) = a(n)+1 + least prime factor of (a(n)+1), according to an observation by Peter Pein, proved by M. F. Hasler, cf. link. - M. F. Hasler, Feb 09 2009 LINKS Peter Pein and M. F. Hasler: Post to the SeqFan list, Feb 09 2009 [From M. F. Hasler, Feb 09 2009] MATHEMATICA a = {2}; Do[ i = a[ [ -1 ] ] + 1; While[ Min[ GCD[ a[ [ -1 ] ], i ], GCD[ a[ [ -1 ] ] + 1, i ] ] == 1, i++ ]; AppendTo[ a, i ], {40} ]; a (* Stefan Steinerberger, Aug 04 2008 *) PROG (PARI) print1(a=2); for(i=2, 99, print1(", "a+=1+factor(a+1)[1, 1])) \\ M. F. Hasler, Feb 09 2009 CROSSREFS Equals A144751 - 1. Sequence in context: A186299 A163777 A215807 * A189804 A246068 A032643 Adjacent sequences:  A140522 A140523 A140524 * A140526 A140527 A140528 KEYWORD nonn AUTHOR Leroy Quet, Jul 02 2008 EXTENSIONS More terms from Stefan Steinerberger, Aug 04 2008 a(42)-a(43) from Ray Chandler, Jun 25 2009 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.