cp's OEIS Frontend

A187209 Sum of all terms of triangle of absolute differences of the divisors of n.

%I A187209 #10 Nov 21 2013 12:50:08
%S A187209 0,1,2,4,4,9,6,11,12,13,10,24,12,21,30,26,16,43,18,40,40,37,22,59,40,
%T A187209 45,50,52,28,89,30,57,60,61,86,90,36,69,70,103,40,125,42,88,140,85,46,
%U A187209 128,84,97,90,106,52,165,130,113,100,109,58,201
%N A187209 Sum of all terms of triangle of absolute differences of the divisors of n.
%C A187209 Note that if n is prime then a(n) = n - 1.
%F A187209 a(n) = A187215(n) - A000203(n).
%e A187209 a(10) = 13 because the divisors of 10 are 1, 2, 5, 10; the triangle of absolute differences is
%e A187209 1, 3, 5;
%e A187209 . 2, 2;
%e A187209 .   0;
%e A187209 and the sum of the terms of triangle is 1+3+5+2+2+0 = 13.
%t A187209 Table[Total[Flatten[NestList[Abs[Differences[#]]&,Differences[Divisors[ n]], DivisorSigma[0,n]-1]]],{n,60}] (* _Harvey P. Dale_, Aug 10 2011 *)
%Y A187209 Cf. A187203, A187205, A187207, A187208.
%K A187209 nonn
%O A187209 1,3
%A A187209 _Omar E. Pol_, Aug 04 2011