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

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A123273 a(0) = 1; a(n) = the number of earlier terms, a(k), where gcd(a(k), a(floor(k/2))) = 1. 1
 1, 1, 2, 3, 4, 4, 4, 5, 6, 6, 6, 6, 6, 6, 6, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS EXAMPLE Among terms a(0) through a(8) (1,1,2,3,4,4,4,5,6), a(0) is coprime to a(0), a(1) is coprime to a(0), a(2) is coprime to a(1), a(3) is coprime to a(1), a(6) is coprime to a(3) and a(7) is coprime to a(3). There are 6 such coprime pairs in the range, so a(9) = 6. MATHEMATICA f[l_List] := Append[l, Count[Table[GCD[l[[k]], l[[Floor[(k + 1)/2]]]], {k, Length[l]}], 1]]; Nest[f, {1}, 80] (* Ray Chandler, Oct 17 2006 *) CROSSREFS Sequence in context: A307467 A145339 A349246 * A284359 A167991 A173073 Adjacent sequences: A123270 A123271 A123272 * A123274 A123275 A123276 KEYWORD nonn AUTHOR Leroy Quet, Oct 10 2006 EXTENSIONS Extended by Ray Chandler, Oct 17 2006 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 December 1 23:44 EST 2022. Contains 358485 sequences. (Running on oeis4.)