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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

Table of n, a(n) for n=0..79.

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: A060740 A307467 A145339 * 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

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Last modified November 11 18:50 EST 2019. Contains 329031 sequences. (Running on oeis4.)