The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A075861 Least k such that (n-k) divides (n+k). 6
 1, 1, 2, 3, 2, 5, 4, 3, 5, 9, 4, 11, 7, 5, 8, 15, 6, 17, 10, 7, 11, 21, 8, 15, 13, 9, 14, 27, 10, 29, 16, 11, 17, 21, 12, 35, 19, 13, 20, 39, 14, 41, 22, 15, 23, 45, 16, 35, 25, 17, 26, 51, 18, 33, 28, 19, 29, 57, 20, 59, 31, 21, 32, 39, 22, 65, 34, 23, 35, 69, 24, 71, 37, 25, 38 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,3 COMMENTS a(n) is also the least k>0 such that F(n-k) divides F(n+k), where F = A000045 (Fibonacci numbers). More generally, if (f(n)) is a divisibility sequence (that is, f(k)|f(n) if and only k|n), then a(n) is the least k>0 such that f(n-k) divides f(n+k). More examples of such f(n): 2^n-1, 3^n-1, n^2, n^3. - Clark Kimberling, Jul 30 2012 LINKS Amiram Eldar, Table of n, a(n) for n = 2..10000 Vaclav Kotesovec, Plot of Sum_{k=1..n} a(k)/n^2 for n = 1..10000 FORMULA Sum_{i=1..n} a(i) is asymptotic to c*n^2, where c = 0.28.... MATHEMATICA Table[i=1; While[!Divisible[n+i, n-i], i++]; i, {n, 2, 100}] (* Harvey P. Dale, Mar 28 2011 *) PROG (PARI) a(n)=if(n<0, 0, s=1; while((n+s)%(n-s)>0, s++); s) CROSSREFS Sequence in context: A317585 A132226 A197702 * A205706 A141658 A350169 Adjacent sequences: A075858 A075859 A075860 * A075862 A075863 A075864 KEYWORD nonn AUTHOR Benoit Cloitre, Oct 15 2002 STATUS approved

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

Last modified August 11 23:45 EDT 2024. Contains 375082 sequences. (Running on oeis4.)