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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. 0

%I

%S 1,1,2,4,6,14,16,44,64,82,88,322,338,982,1002,1006,2456,6428,6766,

%T 19622,19710,19728,19874,98556,105322,126042,126510,252610,253612,

%U 1061208,1061210,3183626,4770276,4770358,4772814,4772828,5939358,31392886

%N 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.

%e 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.

%t 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 *)

%Y Cf. A126260.

%K nonn

%O 1,3

%A _Leroy Quet_, Dec 25 2006

%E Extended by _Ray Chandler_, Dec 26 2006

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Last modified August 9 22:52 EDT 2020. Contains 336335 sequences. (Running on oeis4.)