cp's OEIS Frontend

A192282 Numbers n such that n and n+1 have same sum of anti-divisors.

%I A192282 #12 Mar 30 2012 18:53:49
%S A192282 1,8,17,120,717,729,957,8097,10785,12057,35817,44817,52863,58677,
%T A192282 59757,76759,95397,102957,114117,119337,182157,206097,215997,230037,
%U A192282 253977,263877,269277,271797,295377,321417,402657,435477,483117,485637,510837,586797,589317
%N A192282 Numbers n such that n and n+1 have same sum of anti-divisors.
%C A192282 Like A002961 but using anti-divisors.
%C A192282 Curiously 957 and 958 have same sum of divisors and same sum of anti-divisors.
%H A192282 Donovan Johnson, <a href="/A192282/b192282.txt">Table of n, a(n) for n = 1..1000</a>
%e A192282 Anti-divisors of 717 are 2, 5, 6, 7, 35, 41, 205, 287, 478 and their sum is 1066.
%e A192282 Anti-divisors of 718 are  3, 4, 5, 7, 35, 41, 205, 287, 479 and their sum is 1066.
%p A192282 with(numtheory);
%p A192282 P:=proc(n)
%p A192282 local a,b,i,k;
%p A192282 b:=2;
%p A192282 for i from 4 to n do
%p A192282   a:=0;
%p A192282   for k from 2 to i-1 do
%p A192282     if abs((i mod k)- k/2) < 1 then a:=a+k; fi;
%p A192282   od;
%p A192282   if a=b then print(i-1); fi;
%p A192282   b:=a;
%p A192282 od;
%p A192282 end:
%p A192282 P(200000);
%Y A192282 Cf. A002961, A066272, A192283.
%K A192282 nonn
%O A192282 1,2
%A A192282 _Paolo P. Lava_, Jul 27 2011
%E A192282 Initial term a(1)=1 inserted, a(2)=9 through a(20)=119337 verified, and a(21)-a(28) added by _John W. Layman_, Aug 04 2011