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A122168 a(1)=1; a(n) is the number of earlier terms, a(k) (1 <= k <= n-1), where gcd(a(k),n) is squarefree. 1
1, 1, 2, 3, 4, 5, 6, 6, 8, 9, 10, 9, 12, 13, 14, 12, 16, 15, 18, 14, 20, 21, 22, 17, 24, 25, 23, 20, 28, 29, 30, 22, 32, 33, 34, 22, 36, 37, 38, 28, 40, 41, 42, 30, 40, 45, 46, 33, 48, 48, 50, 35, 52, 48, 54, 37, 56, 57, 58, 40, 60, 61, 56, 41, 64, 65, 66, 44, 68, 69, 70, 41, 72 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..73.

EXAMPLE

(1,1,2,3,4,1,6,6,4,3,2) is gcd(a(k),12), for 1 <= k <= 11. Of these integers, nine are squarefree, so a(12) = 9.

MATHEMATICA

sf[n_] := Max @@ Last /@ FactorInteger[n] < 2; f[s_] := Append[s, Length @ Select[s, sf[GCD[ #, Length[s] + 1]] &]]; Nest[f, {1}, 40] (* Ray Chandler, Aug 24 2006 *)

CROSSREFS

Cf. A122169.

Sequence in context: A061468 A084766 A128559 * A017856 A087412 A024684

Adjacent sequences:  A122165 A122166 A122167 * A122169 A122170 A122171

KEYWORD

nonn

AUTHOR

Leroy Quet, Aug 23 2006

EXTENSIONS

Extended by Ray Chandler, Aug 24 2006

STATUS

approved

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Last modified August 5 21:18 EDT 2020. Contains 336213 sequences. (Running on oeis4.)