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!)
 A089266 Rational knots of determinant 2n+1, counting chiral pairs twice. 1
 2, 3, 4, 4, 6, 7, 6, 9, 10, 8, 12, 11, 10, 15, 16, 12, 14, 19, 14, 21, 22, 14, 24, 22, 18, 27, 22, 20, 30, 31, 20, 26, 34, 24, 36, 37, 22, 32, 40, 28, 42, 34, 30, 45, 38, 32, 38, 49, 32, 51, 52, 28, 54, 55, 38, 57, 46, 38, 50, 56, 42, 51, 64, 44, 66, 56 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 A. Stoimenow, Square numbers, spanning trees and invariants of rational knots (2000) FORMULA a(n) = 1/2 * (A037225(n) + A034444(2*n+1)). MATHEMATICA a[n_] := (EulerPhi[2*n+1] + 2^PrimeNu[2*n+1])/2; Table[a[n], {n, 1, 66}] (* Jean-François Alcover, Oct 11 2013, after Pari *) PROG (PARI) a(n)=(eulerphi(2*n+1)+2^omega(2*n+1))/2 CROSSREFS Cf. A078477, A078478, A018240, A051449, A051766. Sequence in context: A177862 A066981 A130043 * A178993 A193768 A205791 Adjacent sequences:  A089263 A089264 A089265 * A089267 A089268 A089269 KEYWORD nonn,easy,nice AUTHOR Ralf Stephan, Oct 30 2003 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.