A122168 - OEIS

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, 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

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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: A343779 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