A124693 - OEIS

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A124693

a(1)=1. a(n+1) = sum a(k), where the sum is over all positive integers k, k <= n, where each positive integer <= k and coprime to k is also coprime to n.

1, 1, 2, 4, 6, 14, 16, 44, 64, 82, 88, 322, 338, 982, 1002, 1006, 2456, 6428, 6766, 19622, 19710, 19728, 19874, 98556, 105322, 126042, 126510, 252610, 253612, 1061208, 1061210, 3183626, 4770276, 4770358, 4772814, 4772828, 5939358, 31392886

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,3

LINKS

Table of n, a(n) for n=1..38.

EXAMPLE

The positive integers k, where k <= 6 and where each positive integer <= k and coprime to k is also coprime to 6, are 1,2,6. So a(7) = a(1)+a(2)+a(6) = 1+1+14 = 16.

MATHEMATICA

f[n_] := Select[ Range[n], GCD[ #, n] == 1 &]; g[n_] := Select[ Range[n], Times @@ GCD[f[ # ], n] == 1 &]; h[l_List] := Append[l, Plus @@ l[[g[Length[l]]]]]; Nest[h, {1}, 38] (* Ray Chandler, Dec 26 2006 *)

CROSSREFS

Cf. A126260.

Sequence in context: A282139 A138307 A323101 * A358671 A095698 A277909

Adjacent sequences: A124690 A124691 A124692 * A124694 A124695 A124696

KEYWORD

nonn

AUTHOR

Leroy Quet, Dec 25 2006

EXTENSIONS

Extended by Ray Chandler, Dec 26 2006

STATUS

approved