

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
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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



