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A211779 a(n) = Sum_{d_<n | n} sigma(d_<n), where d_<n = divisors of n that are less than n, sigma(x) = A000203(x). 5

%I

%S 0,1,1,4,1,8,1,11,5,10,1,27,1,12,11,26,1,33,1,35,13,16,1,70,7,18,18,

%T 43,1,68,1,57,17,22,15,107,1,24,19,92,1,84,1,59,48,28,1,161,9,59,23,

%U 67,1,112,19,114,25,34,1,217,1,36,58,120,21,116,1,83,29

%N a(n) = Sum_{d_<n | n} sigma(d_<n), where d_<n = divisors of n that are less than n, sigma(x) = A000203(x).

%C The numbers n < 1000 such that n divides a(n) are 4, 10, 42, and 90. (See A224488).

%H Antti Karttunen, <a href="/A211779/b211779.txt">Table of n, a(n) for n = 1..27144</a> (first 1000 terms from Jaroslav Krizek)

%H <a href="/index/Su#sums_of_divisors">Index entries for sequences related to sums of divisors</a>

%F a(n) = A007429(n) - A000203(n) = A211780(n) - A000203(n) + n.

%F G.f.: sum(n>=1, A000203(n)*x^(2*n)/(1-x^n) ). - _Mircea Merca_, Feb 26 2014

%F a(n) = Sum_{d|n} A001065(d). - _Antti Karttunen_, Nov 13 2017

%p with(numtheory);

%p A211779:= proc(q)

%p local b,d,j,n;

%p for n from 1 to q do

%p b:=divisors(n); d:=add(sigma(b[j]),j=1..nops(b))-sigma(n);

%p if trunc(d)=d then print(d);

%p fi; od; end:

%p A211779(10000); # _Paolo P. Lava_, Feb 01 2013

%t Table[Sum[DivisorSigma[1, d], {d, Most[Divisors[n]]}], {n, 100}] (* _T. D. Noe_, Apr 26 2012 *)

%o (PARI) a(n)=sumdiv(n,d,sigma(d))-sigma(n) \\ _Charles R Greathouse IV_, Feb 19 2013

%Y Cf. A000203, A007429, A001065, A211780, A224488.

%K nonn

%O 1,4

%A _Jaroslav Krizek_, Apr 20 2012

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Last modified January 24 04:35 EST 2020. Contains 331183 sequences. (Running on oeis4.)