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Partial sums of A085731.
2

%I #17 Feb 14 2016 14:37:39

%S 1,2,3,7,8,9,10,14,17,18,19,23,24,25,26,42,43,46,47,51,52,53,54,58,63,

%T 64,91,95,96,97,98,114,115,116,117,129,130,131,132,136,137,138,139,

%U 143,146,147,148,164,171,176,177,181,182,209,210,214,215,216,217

%N Partial sums of A085731.

%H Peter Kagey, <a href="/A268398/b268398.txt">Table of n, a(n) for n = 1..10000</a>

%H Project Euler, <a href="https://projecteuler.net/problem=484">Problem 484: Arithmetic Derivative</a>

%t Accumulate@ Table[GCD[n, If[Abs@ n < 2, 0, n Total[#2/#1 & @@@ FactorInteger@ Abs@ n]]], {n, 58}] (* _Michael De Vlieger_, Feb 14 2016, after _Michael Somos_ at A003415 *)

%t Accumulate@ Table[GCD[n, If[Abs@ n < 2, 0, n Total[#2/#1 & @@@ FactorInteger@ Abs@ n]]], {n, 58}] (* _Michael De Vlieger_, Feb 14 2016 *)

%o (Ruby)

%o require 'prime'

%o def a003415(n)

%o return 0 if n == 1

%o return 1 if Prime.prime?(n)

%o a = Prime.each.find { |i| n % i == 0 }

%o a * a003415(n/a) + n/a * a003415(a)

%o end

%o def a268398(n)

%o sum = 0

%o (1..n).map { |n| sum += a003415(n).gcd(n) }.last

%o end

%o (PARI) a085731(n) = {my(f = factor(n)); for (i=1, #f~, if (f[i,2] % f[i,1], f[i,2]--);); factorback(f);}

%o a(n) = sum(k=1, n, a085731(k)); \\ _Michel Marcus_, Feb 14 2016

%Y Cf. A003415, A085731.

%K nonn

%O 1,2

%A _Peter Kagey_, Feb 03 2016